EBay Case Study Example | Topics and Well Written Essays - 250 words

EBay - Case Study Example eBay’s fee structure is based on the principle of charging more for the initial amount and less for additional ones. It is therefore focused more on building big with bulk sales, which indeed exponentially increases on the sales graphs for an organization. The high volume sellers get attracted and even companies that have made it huge within the industry now bank on eBay for their inventory sale (Munir, 2010). As of today, eBay’s fee structure needs no tinkering because it takes care of both the buyers’ and sellers’ needs. Hence incremental improvements can always be brought about but no wholesale changes would as such be required at this stage. The next steps for eBay are to acquire renowned businesses that exist in the virtual world and build on the strategy to take over companies for its own betterment and in a desire to increase profits in the long run. The capabilities shall continue to expand in the times to come which would further the cause of eBay and enhance its vision to grow and expand across the board. It continues to grow when there is a need for both the buyers and sellers to get in touch through a collective mindset of growth and advancement whereby eBay benefits just about everyone who comes in contact with it (Reuer, 2009). This growth comes from a collective mesh of connecting with eBay which paves avenues for such participation which in the end increases on the profits for

Correctional Education Essay Example | Topics and Well Written Essays - 3000 words

Correctional Education - Essay Example This assumes that employment is a major contributing factor to criminal activity and recidivism, on the one hand, and that there is a direct correlation between education and employment, on the other. Both theory and empirical studies have affirmed the imperatives of embracing correctional education as a strategy for the reduction of recidivism. Through a critical analysis of both theory, primarily focusing on the works of Chlup, Shobe and Spry, this section of the research will examine the following: how beneficial it is for correctional educators and others (counselors, correctional officers, other prison officials, etc.) to work together to provide a viable learning experience for institutionalized learners, Criminologists and politicians have debated the effectiveness of correctional rehabilitation programs since the mid-1970s when criminal justice scholars and policy makers throughout the United States embraced the conventional wisdom that 'nothing works' (Lipton, Martinson and Wilks, 1975). Programs based around punishment and surveillance grew. They are being embraced even stronger today despite the fact that Martinson later admitted that he was wrong (1979). An ample amount of research exists that suggests that there are successful programs available to reduce future criminality of not only offenders but also of potential offenders. These studies, amongst which we may cite the works of Chlup, Shobe and Spry, argue that prison education programs are representative of the "normalizing" prison programs whose intent is to increase prison safety and to decrease recidivism. The efficacy of these programs, as Chlup (2004; 2006) contends, has been affirmed and re-affirmed through the long history of education in female penitentiaries, versus the male ones, and the significantly lower rates of female versus male recidivism. Education contributes to the reduction of recidivism and, indeed, is correctional in the real sense of the word because, as may be inferred from all of Shobe (2003), Spry (2003) and Chlup's (2004; 2006) studies, it does not simply provide incarcerated adults with the tools requisite for a crime-less life following release but it teaches them what it means to be a member of society and that respect for society is an expression of self-respect and a determinant of the respect which one will evoke from others. Education within the prison context, in other words, is not just about providing the incarcerated with the skills necessary for later employment but is about social rehabilitation and healthy social development. Penitentiaries do not facilitate social rehabilitation. Sykes (1956) highlighted this last more than five decades ago through his identification and

EBay Case Study Example | Topics and Well Written Essays - 250 words

EBay - Case Study Example eBay’s fee structure is based on the principle of charging more for the initial amount and less for additional ones. It is therefore focused more on building big with bulk sales, which indeed exponentially increases on the sales graphs for an organization. The high volume sellers get attracted and even companies that have made it huge within the industry now bank on eBay for their inventory sale (Munir, 2010). As of today, eBay’s fee structure needs no tinkering because it takes care of both the buyers’ and sellers’ needs. Hence incremental improvements can always be brought about but no wholesale changes would as such be required at this stage. The next steps for eBay are to acquire renowned businesses that exist in the virtual world and build on the strategy to take over companies for its own betterment and in a desire to increase profits in the long run. The capabilities shall continue to expand in the times to come which would further the cause of eBay and enhance its vision to grow and expand across the board. It continues to grow when there is a need for both the buyers and sellers to get in touch through a collective mindset of growth and advancement whereby eBay benefits just about everyone who comes in contact with it (Reuer, 2009). This growth comes from a collective mesh of connecting with eBay which paves avenues for such participation which in the end increases on the profits for

Determining Causes and Effects Assignment Example | Topics and Well Written Essays - 1000 words

Determining Causes and Effects - Assignment Example This paper seeks to establish the major causes of stress and their subsequent effects on college students. In order to achieve this, the paper will categorize stress into a number of classes. These categories are broad representations of the underlying stress causing factors which will be subsequently broken down to give an insight on the stressors. The college environment is a dynamic mix of students from different cultural backgrounds and orientations. These students are meant to interact within the school environment. These interactions could be based on curricular or extra-curricular activities. The transitional approach to college life requires that the student adapt to the new college environment. Freshmen for instance are known to experience heightened levels of stress in trying to settle in to the new dimensions of college life. The students are required to learn interpersonal skills that will enable them cope with other students from diverse cultural backgrounds. Due to the diversity in culture orientations, conflicts are meant to arise. The occurrence of conflicts is commonplace in any society. The most important thing however is finding a way to resolve these conflicts. Unresolved conflicts that arise due to interpersonal interactions between students lead to substantial increase in stress levels (Wright, 1967). An individual is a complex assembly of different faculties, the body, and the soul. The individual ultimate end is achieving happiness. The intricate mix of the body and soul play an integral role in achieving this ultimate end. All the actions an individual engages in are meant to derive some form of satisfaction and happiness to the individual. In the event that the individual engages in activities that fail to realize this objective, then he/she is stressed. Intrapersonal factors refer to the mix of factors that shape the path that an

Ethics and Legal Environment Essay Example for Free

Ethics and Legal Environment Essay Something’s Rotten in Hondo is a case wherein a plant manager, George Mackee, needs to decide whether to get rid of the charges inflicted by the Environmental Protection Agency or EPA or to move in Mexico. He is in a dilemma because if he would choose the former, he has very little chance of eliminating the problem since Bill, George boss, refuses to finance the cleaning of the smokestack. On the other hand, if he would choose the latter, he has to lay off his current employees and hire Mexican workers as a trade-off for not being reprimanded about the EPA standards. His boss leaves the decision up to him. The most obvious ethical concerns in this case are two-fold. The first one is that if George would choose the first option – that is to devise a strategy or a technique that would eradicate the problem with the fines imposed by EPA, he would have to follow what his contemporaries are doing – that is by scheduling the heavy emissions of smokestack during nighttime when the EPA is not in patrol. This entails that he would allow the severance of the environmental pollution (particularly air pollution) for the exchange of not paying any fines to EPA. On the contrary, if George would choose the second option – that is to relocate in Mexico, he would have to dismiss most of his current employees in place of the Mexican workers. And such would include the laying off of his friends and extended families. Furthermore, if he would choose the second option, he would be tolerant of the air pollution caused by the plant’s incapacity to reduce air pollutants. In effect, George has also eliminated the problem of the company on fines issued by EPA. Application of Ethical Theories The case presented in this paper suggests particular ethical problems. For this matter, the author presents two distinct ethical dilemmas for George to decide on: Should he decide to relocate the plant to Mexico or should he just follow the strategy used by his contemporaries? But before he could arrive to a decision, he must first analyze the pros and cons of his decision. If he would choose the former, he could really eliminate the problem with the imposition of fines by the EPA since Mexico assure him that it would not reprimand the plant whatever it does. The only thing is that he has to hire Mexican workers that which implies laying off of his present employees including his friends and extended families. Conversely, if he would agree with that proposal he would also have to bear the dreadful effects of the plant’s operations on the environment, particularly on U. S. Nonetheless, if he would choose the latter, he could also get rid of the problem with the fines imposed by EPA because of failure to meet its guidelines. However, he has to take so much risk by doing the same strategy being used by his contemporaries. In addition, he also has to endure the environmental effects of such strategy just to avoid being reprimanded again by EPA and his boss. Kantian Categorical Imperative If he would apply Kantian’s Categorical Imperative that is by doing his duty, he ought not to do the strategy utilized by his contemporaries (his first option). This is for the reason that he has a duty to protect the environment for both the present and future generations. Plus the fact that his workers have to suffer if he would fire them out of their works. Kant’s Categorical Imperative suggests two maxims in which a person could use to examine the morality of his action. The first maxim states that an action is morally right if one could make such action a universal law. This means that if one could make his action universal or applicable to all others by making it a rule then such action is morally accepted thus it is right. The second maxim, in contrast, focuses on the idea of always treating all human persons as ends and never as means to an end. This maxim argues that every human person has dignity to be respected and has rights as a human thus everyone must act in promoting others rights and not promoting harm to them On the other hand, Kant would not also choose the second option because it also implies environmental degradation. Though he avoids being fined by EPA as well as not even being reprimanded by EPA whatever their operation is, for Kant, he would fail to do the maxims under the Categorical Imperative. He could never make his action or decision as a universal law. Likewise, he would treat other people as mere instruments to achieve his goal by inflicting heath hazards due to smokestack emissions. Kant would suggest that George must never make a decision that would tend to harm the environment because such would also cause severe consequences to the people. As evident in the two options, both would result to the degradation of the environment. Thus, Kant would say that George decision, whichever of the two, would be unethical and morally wrong. Kant would recommend that George must be able to find ways that would not lead to the toleration of environmental pollution. For example, George could instead convince his boss that the only way to solve the problem that would not require him to sacrifice the welfare of the environment is to invest for new technologies that would lessen the emission of smokestack. And such would not even require new scrubbers. Such action is a long-term advantage for the company as well as for the environment. Mill’s Utilitarianism JS Mill’s Utilitarianism would even strengthen the position of not deciding on either of the two options since both would result to environmental pollution. Mill’s Utilitarianism is premised on the idea that an action is right if it promotes the greatest happiness for the greatest number. In other words, Utilitarian principle is mainly directed towards the social utility of an act. This means that if an action can benefit or inflict advantages to more people then such action is morally right. In the case of George, either of the two options would make him tolerate the harm done against the environment. Environment is an essential mechanism that is necessary for human survival. If he would choose the first or the latter option as his decision, he could save the company but inflict great harm to more number of people. Mill would say that George must devise a way in which he could settle the crisis in the company without sacrificing the environment because lots people, including him and his family, depend on the environment’s gifts. Thus, Mill would also recommend the same thing as Kant. Convince his boss by arguing that it is risky and detrimental to the environment if he would follow what his contemporaries are doing. If EPA would find out such underground activities, the company could even be sanctioned more than the imposition of fines. The same thing goes with the second option. If the government of U. S. would find out that the company’s operation cause harsh effects to their environment then there is a big possibility that U. S. would inflict undesirable measures against the company. Rights-based Theory on Decision-making The rights-based theories suggest that it is not always the case that the morality of an action is based on the great benefit that it can produce. At the same time, the rights-based theories do not solely advocate the respect of rights of human persons. These theories suggest that while everyone has a duty to recognize and value the rights of other people (negative rights); it is also everyone’s duty to promote for other’s goals (positive rights). In such manner, the contending ethical theories of Kantianism and Utilitarianism are reconciled in a way that both their concerns are being considered. In the first place, rights are inviolable. They are inalienable or cannot be taken away from human persons no matter what the situation is. Thus, there is no sufficient and rational reason to go against their rights without their consent. The rights-based theories are premised on the idea that every person has the right to choose on how he would like to live his own life. It is not only a person’s duty to respect these rights but also to promote the accomplishment of the goals of other people. By doing so, the rights defined earlier are more strengthen and more realized. In the case of Hondo, George, as a manager, has a duty towards the company. Still, he has duty towards other people. Choosing either of the two decisions would disrespect the rights and disregard the goals of these people. For the rights-based theories, such decision is unethical. The more appropriate way to solve the problem is for George to lend money from a bank so as to install new technology that would lessen the emission of smokestack. He does not really need to hire new scrubbers. By having new technology, for instance machines that clean smokestack, he would not have to result to environmental pollution. It is costly in the beginning but its benefits would be greatly appreciated in the long run. Justice-based Theories in Decision-making In justice-based theories, the overriding principle is focus on the idea of fair. According to John Rawls, the morality of an action can only be measured by appealing to the principle of justice. In his A Theory of Justice, he suggests two principles: liberty and wealth. The former is expressed to explain justice by saying that all must have an equal extent in which they can enjoy and practice their liberties. A least extensive curtailment of liberty is advocated on the condition that such would be shared by all. This entails that an act is right is the product of such act is amenable to all. Hence, justice, in such context, is morally right. In resolving the ethical dilemma faced by George, Justice-based theories would advice him to consider if his decision would be fair to all. Obviously, both options are not beneficial to all. And at the same time, these two options are not the only available options which George has. If he would employ either one of the two options, he would not be just; knowing that if he would be in the place of other people who depend on and survive through environment he would not also endure such nor be willing to agree with such idea. It could be the case that the he and the company are amenable to either of the two options. Nevertheless, others are not really disposed to accept such. Hence, George must not employ such decisions. For George, he could, instead, make control-strategies that would monitor and regulate the emission of smokestack before, during, and even after the plant’s operation in order to examine well the problems concerning the smokestack. Furthermore he could meet with his workers and discuss the problem. He may solicit suggestions on how they could lessen the pollution secreted by their plant onto the environment. After that, he may ask for support from banks by lending or getting loan. Kohlberg’s Moral Development Lawrence Kohlberg was from the line of Piaget who used moral framework to discuss the psychological development of a human person. His thesis on Moral Development suggests that there are six stages wherein a person passes through before he reaches the ultimate state of being a moral person. This theory will be used to show how Kohlberg’s method would help George in resolving his faced ethical dilemma. The first stage is focus on the idea that one person is initially instructed to obey laws such that he could avoid punishment. This is the primary conception on morality that a person has during his early years. With regards to the case presented in this paper, the appeal to laws and rules concerning environmental protection is the most obvious consideration for George’s decision. He would not decide either of the two options since both would make him violate the law regarding the protection of the environment. On the other hand, if he fails to solve the problem immediately, he might receive punishment from his boss (i. e. termination or demotion). The point is that which of the two punishments could George endure more? More likely than not, he would choose not be imprisoned than being demoted or terminated by his boss. The second stage suggests that every person has his own way of thinking which makes every topic or matter subjective to each person. The thing that works for someone or the thing that is considered right by someone may not be the same for another person. Thus, morality in this stage is relative. George could say that the least that he could that would benefit him and put him out of the dilemma that he is in is by either doing the first option or the second option. Both would mean resolution of his problem yet would cause damage to the environment. If he is a nature-lover he would not go for such decision. But if he is a money-lover, he would employ one of the two alternatives. The third stage is concern on the character in which a person thinks of ways on how he can do good things to the persons close to him (e. . family and friends). This means that his initial moral outlook is directed towards the things that he can do for the sake of his loved ones. In the case, if George is at this stage, he would be more inclined to decide and act so as to promote his family and friends’ welfare. Thus, if he would decide on his problem, he would not choose to relocate since his wife is not in favor of this idea and such will inflict great personal unhappiness to his friends who work in the plant.

Concepts of Object Oriented Techniques with OO Issues

Concepts of Object Oriented Techniques with OO Issues Abstract Object-oriented frameworks offer reuse at a high design level promising several benefits to the development of complex systems. This paper sought to 1) define the concepts of object oriented techniques in addition with the OO issues, development techniques and concepts of object oriented programming, it is also introduced the UML as an ordinary and key tool for object-oriented design, additionally 2) we look further into the frameworks from the perspective of object-oriented techniques. In this section, it is aimed to define a reasonable promise between object oriented technology and frameworks. At the end, some future horizons for object oriented technology and frameworks are presented. I. Introduction Computing power and network bandwidth have increased dramatically over the past decade. However, the design and implementation of complex software remains expensive and error-prone. Much of the cost and effort stems from the continuous re-discovery and re-invention of core concepts and components across the software industry. In particular, the growing heterogeneity of hardware architectures and diversity of operating system and communication platforms makes it hard to build correct, portable, efficient, and inexpensive applications from scratch. Object-oriented (OO) techniques and frameworks are promising technologies for reifying proven software designs and implementations in order to reduce the cost and improve the quality of software. A framework is a reusable, semi-complete application that can be specialized to produce custom applications [19]. In contrast to earlier OO reuse techniques based on class libraries, frameworks are targeted for particular business units (such as dat a processing or cellular communications[1]) and application domains (such as user interfaces or real-time avionics). Frameworks like MacApp, ET++, Interviews, ACE, Microsofts MFC and DCOM, JavaSofts RMI, and implementations of OMGs CORBA play an increasingly important role in contemporary software development. II. Object oriented concepts and techniques History The concept of objects and instances in computing had its first major breakthrough with the PDP-1 system at MIT which was probably the earliest example of capability based architecture. Another early example was Sketchpad created by Ivan Sutherland in 1963; however, this was an application and not a programming paradigm. Objects as programming entities were introduced in the 1960s in Simula 67, a programming language designed for performing simulations, created by Ole-Johan Dahl and Kristen Nygaard of the Norwegian Computing Center in Oslo. (They were working on ship simulations, and were confounded by the combinatorial explosion of how the different attributes from different ships could affect one another. The idea occurred to them of grouping the different types of ships into different classes of objects; each class of objects being responsible for defining its own data and behavior.) Such an approach was a simple extrapolation of concepts earlier used in analog programming. On ana log computers, mapping from real-world phenomena/objects to analog phenomena/objects (and conversely), was (and is) called simulation. Simula not only introduced the notion of classes, but also of instances of classes, which is probably the first explicit use of those notions. The ideas of Simula 67 influenced many later languages, especially Smalltalk and derivatives of Lisp and Pascal. The Smalltalk language, which was developed at Xerox PARC[2] (by Alan Kay and others) in the 1970s, introduced the term object-oriented programming to represent the pervasive use of objects and messages as the basis for computation. Smalltalk creators were influenced by the ideas introduced in Simula 67, but Smalltalk was designed to be a fully dynamic system in which classes could be created and modified dynamically rather than statically as in Simula 67. Smalltalk and with it OOP were introduced to a wider audience by the August 1981 issue of Byte magazine. In the 1970s, Kays Smalltalk work had influenced the Lisp community to incorporate object-based techniques which were introduced to developers via the Lisp machine. Experimentation with various extensions to Lisp (like LOOPS and Flavors introducing multiple inheritance and mixins), eventually led to the Common Lisp Object System (CLOS, a part of the first standardized object-oriented programming language, ANSI Common Lisp), which integrates functional programming and object-oriented programming and allows extension via a Meta-object protocol. In the 1980s, there were a few attempts to design processor architectures which included hardware support for objects in memory but these were not successful. Examples include the Intel iAPX 432 and the Linn Smart Rekursiv. Object-oriented programming developed as the dominant programming methodology during the mid-1990s, largely due to the influence of Visual FoxPro 3.0 or possibly C++. Its dominance was further enhanced by the rising popularity of graphical user interfaces, for which object-oriented programming seems to be well-suited. An example of a closely related dynamic GUI library and OOP language can be found in the Cocoa frameworks on Mac OS X, written in Objective-C, an object-oriented, dynamic messaging extension to C based on Smalltalk. OOP toolkits also enhanced the popularity of event-driven programming (although this concept is not limited to OOP). Some feel that association with GUIs (real or perceived) was what propelled OOP into the programming mainstream. At ETH ZÃ ¼rich, Niklaus Wirth and his colleagues had also been investigating such topics as data abstraction and modular programming (although this had been in common use in the 1960s or earlier). Modula-2 (1978) included both, and their succeeding design, Oberon, included a distinctive approach to object orientation, classes, and such. The approach is unlike Smalltalk, and very unlike C++. Object-oriented features have been added to many existing languages during that time, including Ada, BASIC, Fortran, Pascal, and others. Adding these features to languages that were not initially designed for them often led to problems with compatibility and maintainability of code. More recently, a number of languages have emerged that are primarily object-oriented yet compatible with procedural methodology, such as Python and Ruby. Probably the most commercially important recent object-oriented languages are Visual Basic.NET (VB.NET) and C#, both designed for Microsofts .NET platform, and Java, developed by Sun Microsystems. VB.NET and C# both support cross-language inheritance, allowing classes defined in one language to subclass classes defined in the other language. Just as procedural programming led to refinements of techniques such as structured programming, modern object-oriented software design methods include refinements such as the use of design patterns, design by contract, and modeling languages (such as UML). The term OOPS, which refers to an object-oriented programming system, was common in early development of object-oriented programming. III. Fundamental concepts and features Class Defines the abstract characteristics of a thing (object), including the things characteristics (its attributes, fields or properties) and the things behaviors (the things it can do, or methods, operations or features). One might say that a class is a blueprint or factory that describes the nature of something. For example, the class Dog would consist of traits shared by all dogs, such as breed and fur color (characteristics), and the ability to bark and sit (behaviors). Classes provide modularity and structure in an object-oriented computer program. A class should typically be recognizable to a non-programmer familiar with the problem domain, meaning that the characteristics of the class should make sense in context. Also, the code for a class should be relatively self-contained (generally using encapsulation). Collectively, the properties and methods defined by a class are called members. Object A pattern (exemplar) of a class. The class Dog defines all possible dogs by listing the characteristics and behaviors they can have; the object Lassie is one particular dog, with particular versions of the characteristics. A Dog has fur; Lassie has brown-and-white fur. Instance One can have an instance of a class; the instance is the actual object created at runtime. In programmer jargon, the Lassie object is an instance of the Dog class. The set of values of the attributes of a particular object is called its state. The object consists of state and the behavior thats defined in the objects class. More on Classes, Metaclasses, Parameterized Classes, and Exemplars There are two broad categories of objects: classes and instances. Users of object-oriented technology usually think of classes as containing the information necessary to create instances, i.e., the structure and capabilities of an instance is determined by its corresponding class. There are three commonly used (and different) views on the definition for class: A class is a pattern, template, or blueprint for a category of structurally identical items. The items created using the class are called instances. This is often referred to as the class as a `cookie cutter' view. As you might guess, the instances are the cookies. A class is a thing that consists of both a pattern and a mechanism for creating items based on that pattern. This is the class as an `instance factory' view; instances are the individual items that are manufactured (created) using the classs creation mechanism. A class is the set of all items created using a specific pattern. Said another way, the class is the set of all instances of that pattern. We should note that it is possible for an instance of a class to also be a class. A metaclass is a class whose instances themselves are classes. This means when we use the instance creation mechanism in a metaclass, the instance created will itself be a class. The instance creation mechanism of this class can, in turn, be used to create instances although these instances may or may not themselves be classes. A concept very similar to the metaclass is the parameterized class. A parameterized class is a template for a class wherein specific items have been identified as being required to create non-parameterized classes based on the template. In effect, a parameterized class can be viewed as a fill in the blanks version of a class. One cannot directly use the instance creation mechanism of a parameterized class. First, we must supply the required parameters, resulting in the creation of a non-parameterized class. Once we have a non-parameterized class, we can use its creation mechanisms to create instances. In this paper, we will use the term class to mean metaclass, parameterized class, or a class that is neither a metaclass nor a parameterized class. We will make a distinction only when it is necessary to do so. Further, we will occasionally refer to non-class instances. A non-class instance is an instance of a class, but is itself not a class. An instance of a metaclass, for example, would not be a non-class instance. In this paper, we will sometimes refer to instantiation. Instantiation has two common meanings: as a verb, instantiation is the process of creating an instance of a class, and as a noun, an instantiation is an instance of a class. Some people restrict the use of the term object to instances of classes. For these people, classes are not objects. However, when these people are confronted with the concepts of metaclasses and parameterized classes, they have a difficulty attempting to resolve the problems these concepts introduce. For example, is a class that is an instance of a metaclass an object even though it is itself a class? In this paper, we will use the term object to refer to both classes and their instances. We will only distinguish between the two when needed. Black Boxes and Interfaces Objects are black boxes. Specifically, the underlying implementations of objects are hidden from those that use the object. In object-oriented systems, it is only the producer (creator, designer, or builder) of an object that knows the details about the internal construction of that object. The consumers (users) of an object are denied knowledge of the inner workings of the object, and must deal with an object via one of its three distinct interfaces: The public interface. This is the interface that is open (visible) to everybody. The inheritance interface. This is the interface that is accessible only by direct specializations of the object. (We will discuss inheritance and specialization later in this chapter.) In class-based object-oriented systems, only classes can provide an inheritance interface. The parameter interface. In the case of parameterized classes, the parameter interface defines the parameters that must be supplied to create an instance of the parameterized class. Another way of saying that an item is in the public interface of an object is to say that the object exports that item. Similarly, when an object requires information from outside of itself (e.g., as with the parameters in a parameterized class), we can say that the object needs to import that information. Aggregation It is, of course, possible for objects to be composed of other objects. Aggregation is either: The process of creating a new object from two or more other objects, or An object that is composed of two or more other objects. For example, a date object could be fashioned from a month object, a day object, and a year object. A list of names object, for example, can be thought of as containing many name objects. A monolithic object is an object that has no externally-discernible structure. Said another way, a monolithic object does not appear to have been constructed from two or more other objects. Specifically, a monolithic object can only be treated as a cohesive whole. Those outside of a monolithic object cannot directly interact with any (real or imagined) objects within the monolithic object. A radio button in a graphical user interface (GUI) is an example of a monolithic object. Composite objects are objects that have an externally-discernible structure, and the structure can be addressed via the public interface of the composite object. The objects that comprise a composite object are referred to as component objects. Composite objects meet one or both of the following criteria: The state of a composite object is directly affected by the presence or absence of one or more of its component objects, and/or The component objects can be directly referenced via the public interface of their corresponding composite object. It is useful to divide composite objects into two subcategories: heterogeneous composite objects and homogeneous composite objects: A heterogeneous composite object is a composite object that is conceptually composed of component objects that are not all conceptually the same. For example, a date (made up of a month object, a day object, and a year object) is a heterogeneous composite object. A homogeneous composite object is a composite object that is conceptually composed of component objects that are all conceptually the same. For example, a list of addresses is a homogeneous composite object. The rules for designing heterogeneous composite objects are different from the rules for designing homogeneous composite objects. Specialization and Inheritance Aggregation is not the only way in which two objects can be related. One object can be a specialization of another object. Specialization is either: The process of defining a new object based on a (typically) more narrow definition of an existing object, or An object that is directly related to, and more narrowly defined than, another object. Specialization is usually associated with classes. It is usually only in the so-called classless object-oriented systems that we think of specialization for objects other than classes. Depending on their technical background, there are a number of different ways in which people express specialization. For example, those who are familiar with an object-oriented programming language called Smalltalk refer to specializations as subclasses and to the corresponding generalizations of these specializations as superclasses. Those with a background in the C++ programming language use the term derived class for specialization and base class for corresponding generalizations. It is common to say that everything that is true for a generalization is also true for its corresponding specialization. We can, for example, define checking accounts and savings accounts as specializations of bank accounts. Another way of saying this is that a checking account is a kind of bank account, and a savings account is a kind of bank account. Still another way of expressing this idea is to say that everything that was true for the bank account is also true for the savings account and the checking account. In an object-oriented context, we speak of specializations as inheriting characteristics from their corresponding generalizations. Inheritance can be defined as the process whereby one object acquires (gets, receives) characteristics from one or more other objects. Some object-oriented systems permit only single inheritance, a situation in which a specialization may only acquire characteristics from a single generalization. Many object-oriented systems, however, allow for multiple inheritance, a situation in which a specialization may acquire characteristics from two or more corresponding generalizations. Our previous discussion of the bank account, checking account, and savings account was an example of single inheritance. A telescope and a television set are both specializations of device that enables one to see things far away. A television set is also a kind of electronic device. You might say that a television set acquires characteristics from two different generalizations, device that enables one to see things far away and electronic device. Therefore, a television set is a product of multiple inheritance. Abstract Classes We usually think of classes as being complete definitions. However, there are situations where incomplete definitions are useful, and classes that represent these incomplete definitions are equally useful. For example, in everyday conversation, we might talk about such items as bank accounts, insurance policies, and houses. In object-oriented thinking, we often isolate useful, but incomplete, concepts such as these into their own special classes. Abstract classes are classes that embody coherent and cohesive, but incomplete, concepts, and in turn, make these characteristics available to their specializations via inheritance. People sometimes use the terms partial type and abstract superclass as synonyms for abstract class. While we would never create instances of abstract classes, we most certainly would make their individual characteristics available to more specialized classes via inheritance. For example, consider the concept of an automobile. On one hand, most people know what an automobile is. On the other hand, automobile is not a complete definition for any vehicle. It would be quite accurate to describe automobile as the set of characteristics that make a thing an automobile, in other words, the essence of automobile-ness. Operations The public interface of an object typically contains three different categories of items: operations (sometimes referred to as method selectors, method interfaces, messages, or methods), constants, and exceptions. An operation in the public interface of an object advertises a functional capability of that object. For example, deposit would be an operation in the public interface of a bank account object, what is current temperature would be an operation in the public interface of a temperature sensor object, and increment would be an operation in the public interface of a counter object. The actual algorithm for accomplishing an operation is referred to as a method. Unlike operations, methods are not in the public interface for an object. Rather, methods are hidden on the inside of an object. So, while users of bank account objects would know that they could make a deposit into a bank account, they would be unaware of the details as to how that deposit actually got credited to the bank account. We refer to the operations in the public interface of an object as suffered operations. Suffered operations are operations that meet two criteria: they are things that happen to an object, and they are in the public interface of that object. For example, we can say that a bank account suffers the operation of having a deposit made into it. The bank account can also suffer the operation of being queried as to its current balance. Some people also refer to suffered operations as exported operations. There are three broad categories of suffered operations, i.e.: A selector is an operation that tells us something about the state of an object, but cannot, by definition, change the state of the object. An operation that tells us the current balance of a bank account is an example of a selector operation. A constructor is an operation that has the ability to change the state of an object. For example, an operation in the public interface to a mailbox object that added a message to the mailbox would be a constructor operation. (Please note that some people restrict the definition of the term constructor to those operations that cause instances of a class to come into existence.) In the context of a homogeneous composite object, an iterator is an operation that allows its users to visit (access) each of the component objects that make up the homogeneous composite object. If we have a list of addresses, for example, and we wish to print the entire list, an iterator would allow us to visit each address object within the list and then, in turn, to print each address. Iterators can be further divided into two broad categories: active (open) iterators and passive (closed) iterators. Active iterators are objects in their own right. Passive iterators are implemented as operations in the interface of the object over which they allow iteration. Passive iterators are further broken down into selective iterators and constructive iterators. Passive selective iterators do not allow their users to change the object over which the iteration takes place. Passive constructive iterators do allow users to change the object over which iteration takes place. We can also describe suffered operations as primitive or composite. A primitive operation is an operation that cannot be accomplished simply, efficiently, and reliably without direct knowledge of the underlying (hidden) implementation of the object. As an example, we could argue that an operation that added an item to a list object, or an operation that deleted an item from a list object were primitive operations with respect to the list object. Suppose that we wanted to create a swap operation, an operation that would swap in a new item in a list, while at the same time swapping out an old item in the same list. This is not a primitive operation since we can accomplish this with a simple combination of the delete operation (deleting the old item) followed by the add operation (adding the new item). The swap operation is an example of a composite operation. A composite operation is any operation that is composed, or can be composed, of two or more primitive operations. Sometimes objects need help in maintaining their characteristics. Suppose, for example, that we wanted to create a generic ordered list object. An ordered list is a list that must order its contents from the smallest to the largest. Specifically, every time we add an item to our ordered list, that item would have to be placed in its proper position with respect to all the other items already in the list. By generic, we mean a template that can be instantiated with the category (class) of items we wish to place in the ordered list. It would not be unreasonable to implement this object as a parameterized class. Obviously, one of the parameters would be the category of items (e.g., class) that we desired to place in the list. For example, could instantiate (make an instance) the generic ordered list with a name class resulting in the creation of an ordered list of names class. There is a problem, however. Given that we could instantiate the generic ordered list with just about any category of items, how can we be sure that the ordered lists will know how to properly maintain order no matter what we use to instantiate the generic ordered list? Suppose, for example, that we wanted an ordered list of fazoomas. How could the generic list class tell if one fazooma was greater than or less than another fazooma? A solution would be for the generic ordered list to require a second parameter, a parameter over and above the category of items (class) that we desired to place in the list. This second parameter would be a The Constants In addition to suffered operations, the public interface of an object can also contain constants. Constants are objects of constant state. Imagine that we want to create a bounded list of addresses class. A bounded list is a list that has a fixed maximum number of elements. A bounded list can be empty, and it can contain fewer than the maximum number of elements. It can even contain the maximum number of elements, but it can never contain more than the defined maximum number of elements. Assume that we place a constant in the public interface of our bounded list of addresses. This constant represents the maximum number of elements that can be placed in the bounded list. Assume also that there is a suffered operation that will tell us how many elements (addresses, in our example) are currently in the bounded list. We can now determine how much room is available in the bounded list by inquiring how many addresses are already in the list, and then subtracting this from the previously-defined constant. In some cases, as with the bounded list example above, constants are provided more for convenience than necessity. In other cases, such as in the case of encryption algorithms needing a seed value, constants are an absolute requirement. Exceptions A third category of items that can be found in the public interface of objects is exceptions. Exceptions have two different definitions: an event that causes suspension of normal application execution, and a set of information directly relating to the event that caused suspension of normal application execution. Exceptions can be contrasted with an older, less reliable technology: error codes. The idea behind error codes was fairly simple. You would request that an application, or part of an application, accomplish some work. One of the pieces of information that would be returned to the requester would be an error code. If all had gone well, the error code would typically have a value of zero. If any problems had occurred, the error code would have a non-zero value. It was also quite common to associate different non-zero values of an error code with specific errors. Error codes suffered from two major problems: No one was forced to actually check the value of returned error codes. Changes (additions, deletions, and modifications) in the meanings of the special values assigned to error codes were not automatically passed on to interested parties. Tracking the effects of a changed error code value often consumed a significant amount of resources. To understand how exceptions directly address both of these issues, we first need to understand how exceptions typically work: Exceptions may be defined by the environment or by the user. When an exceptional (but not unforeseen) condition occurs, an appropriate exception is activated. (People use different terms to express the activation of an exception. The most common is raise. Less commonly, people use the terms throw or activate.) This activation may be automatic (controlled by the environment) or may be expressly requested by the designer of the object or application. Examples of exceptional conditions include trying to remove something from an empty container, directing an elevator on the top floor to go up, and attempting to cause a date to take on an invalid value like February 31, 1993. Once the exception is activated, normal application execution stops and control is transferred to a locally defined exception handler, if one is present. If no locally defined exception handler is present or if the exception handler is not equipped to handle the exception, the exception is propagated to the next higher level of the application. Exceptions cannot be ignored. An exception will continue to be sent to higher levels of the application until it is either turned off or the application ceases to function. An exception handler checks to see what type of exception has been activated. If the exception is one that the handler recognizes, a specific set of actions is taken. Executing a set of actions in response to an exception is known as handling the exception. Handling an exception deactivates the exception; the exception will not be propagated any further. Unlike error codes, exceptions cannot be ignored. Once an exception has been activated, it demands attention. In object-oriented systems, exceptions are placed in the public interfaces of objects. Changes in the public interfaces of objects very often require an automatic rechecking of all other objects that invoke operations in the changed objects. Thus, changes in exceptions result in at least a partially automated propagation of change information. Object Coupling and Object Cohesion Engineers have known for centuries that the less any one part of a system knows about any other part of that same system, the better the overall system. Systems whose components are highly independent of each other are easier to fix and enhance than systems where there are strong interdependencies among some or all of the components. Highly independent system components are possible when there is minimal coupling among the components, and each component is highly cohesive. Coupling is a measure of the strength of the connection between any two system components. The more any one component knows about another component, the tighter (worse) the coupling is between those two components. Cohesion is a measure of how logically related the parts of an individual component are to each o Concepts of Object Oriented Techniques with OO Issues Concepts of Object Oriented Techniques with OO Issues Abstract Object-oriented frameworks offer reuse at a high design level promising several benefits to the development of complex systems. This paper sought to 1) define the concepts of object oriented techniques in addition with the OO issues, development techniques and concepts of object oriented programming, it is also introduced the UML as an ordinary and key tool for object-oriented design, additionally 2) we look further into the frameworks from the perspective of object-oriented techniques. In this section, it is aimed to define a reasonable promise between object oriented technology and frameworks. At the end, some future horizons for object oriented technology and frameworks are presented. I. Introduction Computing power and network bandwidth have increased dramatically over the past decade. However, the design and implementation of complex software remains expensive and error-prone. Much of the cost and effort stems from the continuous re-discovery and re-invention of core concepts and components across the software industry. In particular, the growing heterogeneity of hardware architectures and diversity of operating system and communication platforms makes it hard to build correct, portable, efficient, and inexpensive applications from scratch. Object-oriented (OO) techniques and frameworks are promising technologies for reifying proven software designs and implementations in order to reduce the cost and improve the quality of software. A framework is a reusable, semi-complete application that can be specialized to produce custom applications [19]. In contrast to earlier OO reuse techniques based on class libraries, frameworks are targeted for particular business units (such as dat a processing or cellular communications[1]) and application domains (such as user interfaces or real-time avionics). Frameworks like MacApp, ET++, Interviews, ACE, Microsofts MFC and DCOM, JavaSofts RMI, and implementations of OMGs CORBA play an increasingly important role in contemporary software development. II. Object oriented concepts and techniques History The concept of objects and instances in computing had its first major breakthrough with the PDP-1 system at MIT which was probably the earliest example of capability based architecture. Another early example was Sketchpad created by Ivan Sutherland in 1963; however, this was an application and not a programming paradigm. Objects as programming entities were introduced in the 1960s in Simula 67, a programming language designed for performing simulations, created by Ole-Johan Dahl and Kristen Nygaard of the Norwegian Computing Center in Oslo. (They were working on ship simulations, and were confounded by the combinatorial explosion of how the different attributes from different ships could affect one another. The idea occurred to them of grouping the different types of ships into different classes of objects; each class of objects being responsible for defining its own data and behavior.) Such an approach was a simple extrapolation of concepts earlier used in analog programming. On ana log computers, mapping from real-world phenomena/objects to analog phenomena/objects (and conversely), was (and is) called simulation. Simula not only introduced the notion of classes, but also of instances of classes, which is probably the first explicit use of those notions. The ideas of Simula 67 influenced many later languages, especially Smalltalk and derivatives of Lisp and Pascal. The Smalltalk language, which was developed at Xerox PARC[2] (by Alan Kay and others) in the 1970s, introduced the term object-oriented programming to represent the pervasive use of objects and messages as the basis for computation. Smalltalk creators were influenced by the ideas introduced in Simula 67, but Smalltalk was designed to be a fully dynamic system in which classes could be created and modified dynamically rather than statically as in Simula 67. Smalltalk and with it OOP were introduced to a wider audience by the August 1981 issue of Byte magazine. In the 1970s, Kays Smalltalk work had influenced the Lisp community to incorporate object-based techniques which were introduced to developers via the Lisp machine. Experimentation with various extensions to Lisp (like LOOPS and Flavors introducing multiple inheritance and mixins), eventually led to the Common Lisp Object System (CLOS, a part of the first standardized object-oriented programming language, ANSI Common Lisp), which integrates functional programming and object-oriented programming and allows extension via a Meta-object protocol. In the 1980s, there were a few attempts to design processor architectures which included hardware support for objects in memory but these were not successful. Examples include the Intel iAPX 432 and the Linn Smart Rekursiv. Object-oriented programming developed as the dominant programming methodology during the mid-1990s, largely due to the influence of Visual FoxPro 3.0 or possibly C++. Its dominance was further enhanced by the rising popularity of graphical user interfaces, for which object-oriented programming seems to be well-suited. An example of a closely related dynamic GUI library and OOP language can be found in the Cocoa frameworks on Mac OS X, written in Objective-C, an object-oriented, dynamic messaging extension to C based on Smalltalk. OOP toolkits also enhanced the popularity of event-driven programming (although this concept is not limited to OOP). Some feel that association with GUIs (real or perceived) was what propelled OOP into the programming mainstream. At ETH ZÃ ¼rich, Niklaus Wirth and his colleagues had also been investigating such topics as data abstraction and modular programming (although this had been in common use in the 1960s or earlier). Modula-2 (1978) included both, and their succeeding design, Oberon, included a distinctive approach to object orientation, classes, and such. The approach is unlike Smalltalk, and very unlike C++. Object-oriented features have been added to many existing languages during that time, including Ada, BASIC, Fortran, Pascal, and others. Adding these features to languages that were not initially designed for them often led to problems with compatibility and maintainability of code. More recently, a number of languages have emerged that are primarily object-oriented yet compatible with procedural methodology, such as Python and Ruby. Probably the most commercially important recent object-oriented languages are Visual Basic.NET (VB.NET) and C#, both designed for Microsofts .NET platform, and Java, developed by Sun Microsystems. VB.NET and C# both support cross-language inheritance, allowing classes defined in one language to subclass classes defined in the other language. Just as procedural programming led to refinements of techniques such as structured programming, modern object-oriented software design methods include refinements such as the use of design patterns, design by contract, and modeling languages (such as UML). The term OOPS, which refers to an object-oriented programming system, was common in early development of object-oriented programming. III. Fundamental concepts and features Class Defines the abstract characteristics of a thing (object), including the things characteristics (its attributes, fields or properties) and the things behaviors (the things it can do, or methods, operations or features). One might say that a class is a blueprint or factory that describes the nature of something. For example, the class Dog would consist of traits shared by all dogs, such as breed and fur color (characteristics), and the ability to bark and sit (behaviors). Classes provide modularity and structure in an object-oriented computer program. A class should typically be recognizable to a non-programmer familiar with the problem domain, meaning that the characteristics of the class should make sense in context. Also, the code for a class should be relatively self-contained (generally using encapsulation). Collectively, the properties and methods defined by a class are called members. Object A pattern (exemplar) of a class. The class Dog defines all possible dogs by listing the characteristics and behaviors they can have; the object Lassie is one particular dog, with particular versions of the characteristics. A Dog has fur; Lassie has brown-and-white fur. Instance One can have an instance of a class; the instance is the actual object created at runtime. In programmer jargon, the Lassie object is an instance of the Dog class. The set of values of the attributes of a particular object is called its state. The object consists of state and the behavior thats defined in the objects class. More on Classes, Metaclasses, Parameterized Classes, and Exemplars There are two broad categories of objects: classes and instances. Users of object-oriented technology usually think of classes as containing the information necessary to create instances, i.e., the structure and capabilities of an instance is determined by its corresponding class. There are three commonly used (and different) views on the definition for class: A class is a pattern, template, or blueprint for a category of structurally identical items. The items created using the class are called instances. This is often referred to as the class as a `cookie cutter' view. As you might guess, the instances are the cookies. A class is a thing that consists of both a pattern and a mechanism for creating items based on that pattern. This is the class as an `instance factory' view; instances are the individual items that are manufactured (created) using the classs creation mechanism. A class is the set of all items created using a specific pattern. Said another way, the class is the set of all instances of that pattern. We should note that it is possible for an instance of a class to also be a class. A metaclass is a class whose instances themselves are classes. This means when we use the instance creation mechanism in a metaclass, the instance created will itself be a class. The instance creation mechanism of this class can, in turn, be used to create instances although these instances may or may not themselves be classes. A concept very similar to the metaclass is the parameterized class. A parameterized class is a template for a class wherein specific items have been identified as being required to create non-parameterized classes based on the template. In effect, a parameterized class can be viewed as a fill in the blanks version of a class. One cannot directly use the instance creation mechanism of a parameterized class. First, we must supply the required parameters, resulting in the creation of a non-parameterized class. Once we have a non-parameterized class, we can use its creation mechanisms to create instances. In this paper, we will use the term class to mean metaclass, parameterized class, or a class that is neither a metaclass nor a parameterized class. We will make a distinction only when it is necessary to do so. Further, we will occasionally refer to non-class instances. A non-class instance is an instance of a class, but is itself not a class. An instance of a metaclass, for example, would not be a non-class instance. In this paper, we will sometimes refer to instantiation. Instantiation has two common meanings: as a verb, instantiation is the process of creating an instance of a class, and as a noun, an instantiation is an instance of a class. Some people restrict the use of the term object to instances of classes. For these people, classes are not objects. However, when these people are confronted with the concepts of metaclasses and parameterized classes, they have a difficulty attempting to resolve the problems these concepts introduce. For example, is a class that is an instance of a metaclass an object even though it is itself a class? In this paper, we will use the term object to refer to both classes and their instances. We will only distinguish between the two when needed. Black Boxes and Interfaces Objects are black boxes. Specifically, the underlying implementations of objects are hidden from those that use the object. In object-oriented systems, it is only the producer (creator, designer, or builder) of an object that knows the details about the internal construction of that object. The consumers (users) of an object are denied knowledge of the inner workings of the object, and must deal with an object via one of its three distinct interfaces: The public interface. This is the interface that is open (visible) to everybody. The inheritance interface. This is the interface that is accessible only by direct specializations of the object. (We will discuss inheritance and specialization later in this chapter.) In class-based object-oriented systems, only classes can provide an inheritance interface. The parameter interface. In the case of parameterized classes, the parameter interface defines the parameters that must be supplied to create an instance of the parameterized class. Another way of saying that an item is in the public interface of an object is to say that the object exports that item. Similarly, when an object requires information from outside of itself (e.g., as with the parameters in a parameterized class), we can say that the object needs to import that information. Aggregation It is, of course, possible for objects to be composed of other objects. Aggregation is either: The process of creating a new object from two or more other objects, or An object that is composed of two or more other objects. For example, a date object could be fashioned from a month object, a day object, and a year object. A list of names object, for example, can be thought of as containing many name objects. A monolithic object is an object that has no externally-discernible structure. Said another way, a monolithic object does not appear to have been constructed from two or more other objects. Specifically, a monolithic object can only be treated as a cohesive whole. Those outside of a monolithic object cannot directly interact with any (real or imagined) objects within the monolithic object. A radio button in a graphical user interface (GUI) is an example of a monolithic object. Composite objects are objects that have an externally-discernible structure, and the structure can be addressed via the public interface of the composite object. The objects that comprise a composite object are referred to as component objects. Composite objects meet one or both of the following criteria: The state of a composite object is directly affected by the presence or absence of one or more of its component objects, and/or The component objects can be directly referenced via the public interface of their corresponding composite object. It is useful to divide composite objects into two subcategories: heterogeneous composite objects and homogeneous composite objects: A heterogeneous composite object is a composite object that is conceptually composed of component objects that are not all conceptually the same. For example, a date (made up of a month object, a day object, and a year object) is a heterogeneous composite object. A homogeneous composite object is a composite object that is conceptually composed of component objects that are all conceptually the same. For example, a list of addresses is a homogeneous composite object. The rules for designing heterogeneous composite objects are different from the rules for designing homogeneous composite objects. Specialization and Inheritance Aggregation is not the only way in which two objects can be related. One object can be a specialization of another object. Specialization is either: The process of defining a new object based on a (typically) more narrow definition of an existing object, or An object that is directly related to, and more narrowly defined than, another object. Specialization is usually associated with classes. It is usually only in the so-called classless object-oriented systems that we think of specialization for objects other than classes. Depending on their technical background, there are a number of different ways in which people express specialization. For example, those who are familiar with an object-oriented programming language called Smalltalk refer to specializations as subclasses and to the corresponding generalizations of these specializations as superclasses. Those with a background in the C++ programming language use the term derived class for specialization and base class for corresponding generalizations. It is common to say that everything that is true for a generalization is also true for its corresponding specialization. We can, for example, define checking accounts and savings accounts as specializations of bank accounts. Another way of saying this is that a checking account is a kind of bank account, and a savings account is a kind of bank account. Still another way of expressing this idea is to say that everything that was true for the bank account is also true for the savings account and the checking account. In an object-oriented context, we speak of specializations as inheriting characteristics from their corresponding generalizations. Inheritance can be defined as the process whereby one object acquires (gets, receives) characteristics from one or more other objects. Some object-oriented systems permit only single inheritance, a situation in which a specialization may only acquire characteristics from a single generalization. Many object-oriented systems, however, allow for multiple inheritance, a situation in which a specialization may acquire characteristics from two or more corresponding generalizations. Our previous discussion of the bank account, checking account, and savings account was an example of single inheritance. A telescope and a television set are both specializations of device that enables one to see things far away. A television set is also a kind of electronic device. You might say that a television set acquires characteristics from two different generalizations, device that enables one to see things far away and electronic device. Therefore, a television set is a product of multiple inheritance. Abstract Classes We usually think of classes as being complete definitions. However, there are situations where incomplete definitions are useful, and classes that represent these incomplete definitions are equally useful. For example, in everyday conversation, we might talk about such items as bank accounts, insurance policies, and houses. In object-oriented thinking, we often isolate useful, but incomplete, concepts such as these into their own special classes. Abstract classes are classes that embody coherent and cohesive, but incomplete, concepts, and in turn, make these characteristics available to their specializations via inheritance. People sometimes use the terms partial type and abstract superclass as synonyms for abstract class. While we would never create instances of abstract classes, we most certainly would make their individual characteristics available to more specialized classes via inheritance. For example, consider the concept of an automobile. On one hand, most people know what an automobile is. On the other hand, automobile is not a complete definition for any vehicle. It would be quite accurate to describe automobile as the set of characteristics that make a thing an automobile, in other words, the essence of automobile-ness. Operations The public interface of an object typically contains three different categories of items: operations (sometimes referred to as method selectors, method interfaces, messages, or methods), constants, and exceptions. An operation in the public interface of an object advertises a functional capability of that object. For example, deposit would be an operation in the public interface of a bank account object, what is current temperature would be an operation in the public interface of a temperature sensor object, and increment would be an operation in the public interface of a counter object. The actual algorithm for accomplishing an operation is referred to as a method. Unlike operations, methods are not in the public interface for an object. Rather, methods are hidden on the inside of an object. So, while users of bank account objects would know that they could make a deposit into a bank account, they would be unaware of the details as to how that deposit actually got credited to the bank account. We refer to the operations in the public interface of an object as suffered operations. Suffered operations are operations that meet two criteria: they are things that happen to an object, and they are in the public interface of that object. For example, we can say that a bank account suffers the operation of having a deposit made into it. The bank account can also suffer the operation of being queried as to its current balance. Some people also refer to suffered operations as exported operations. There are three broad categories of suffered operations, i.e.: A selector is an operation that tells us something about the state of an object, but cannot, by definition, change the state of the object. An operation that tells us the current balance of a bank account is an example of a selector operation. A constructor is an operation that has the ability to change the state of an object. For example, an operation in the public interface to a mailbox object that added a message to the mailbox would be a constructor operation. (Please note that some people restrict the definition of the term constructor to those operations that cause instances of a class to come into existence.) In the context of a homogeneous composite object, an iterator is an operation that allows its users to visit (access) each of the component objects that make up the homogeneous composite object. If we have a list of addresses, for example, and we wish to print the entire list, an iterator would allow us to visit each address object within the list and then, in turn, to print each address. Iterators can be further divided into two broad categories: active (open) iterators and passive (closed) iterators. Active iterators are objects in their own right. Passive iterators are implemented as operations in the interface of the object over which they allow iteration. Passive iterators are further broken down into selective iterators and constructive iterators. Passive selective iterators do not allow their users to change the object over which the iteration takes place. Passive constructive iterators do allow users to change the object over which iteration takes place. We can also describe suffered operations as primitive or composite. A primitive operation is an operation that cannot be accomplished simply, efficiently, and reliably without direct knowledge of the underlying (hidden) implementation of the object. As an example, we could argue that an operation that added an item to a list object, or an operation that deleted an item from a list object were primitive operations with respect to the list object. Suppose that we wanted to create a swap operation, an operation that would swap in a new item in a list, while at the same time swapping out an old item in the same list. This is not a primitive operation since we can accomplish this with a simple combination of the delete operation (deleting the old item) followed by the add operation (adding the new item). The swap operation is an example of a composite operation. A composite operation is any operation that is composed, or can be composed, of two or more primitive operations. Sometimes objects need help in maintaining their characteristics. Suppose, for example, that we wanted to create a generic ordered list object. An ordered list is a list that must order its contents from the smallest to the largest. Specifically, every time we add an item to our ordered list, that item would have to be placed in its proper position with respect to all the other items already in the list. By generic, we mean a template that can be instantiated with the category (class) of items we wish to place in the ordered list. It would not be unreasonable to implement this object as a parameterized class. Obviously, one of the parameters would be the category of items (e.g., class) that we desired to place in the list. For example, could instantiate (make an instance) the generic ordered list with a name class resulting in the creation of an ordered list of names class. There is a problem, however. Given that we could instantiate the generic ordered list with just about any category of items, how can we be sure that the ordered lists will know how to properly maintain order no matter what we use to instantiate the generic ordered list? Suppose, for example, that we wanted an ordered list of fazoomas. How could the generic list class tell if one fazooma was greater than or less than another fazooma? A solution would be for the generic ordered list to require a second parameter, a parameter over and above the category of items (class) that we desired to place in the list. This second parameter would be a The Constants In addition to suffered operations, the public interface of an object can also contain constants. Constants are objects of constant state. Imagine that we want to create a bounded list of addresses class. A bounded list is a list that has a fixed maximum number of elements. A bounded list can be empty, and it can contain fewer than the maximum number of elements. It can even contain the maximum number of elements, but it can never contain more than the defined maximum number of elements. Assume that we place a constant in the public interface of our bounded list of addresses. This constant represents the maximum number of elements that can be placed in the bounded list. Assume also that there is a suffered operation that will tell us how many elements (addresses, in our example) are currently in the bounded list. We can now determine how much room is available in the bounded list by inquiring how many addresses are already in the list, and then subtracting this from the previously-defined constant. In some cases, as with the bounded list example above, constants are provided more for convenience than necessity. In other cases, such as in the case of encryption algorithms needing a seed value, constants are an absolute requirement. Exceptions A third category of items that can be found in the public interface of objects is exceptions. Exceptions have two different definitions: an event that causes suspension of normal application execution, and a set of information directly relating to the event that caused suspension of normal application execution. Exceptions can be contrasted with an older, less reliable technology: error codes. The idea behind error codes was fairly simple. You would request that an application, or part of an application, accomplish some work. One of the pieces of information that would be returned to the requester would be an error code. If all had gone well, the error code would typically have a value of zero. If any problems had occurred, the error code would have a non-zero value. It was also quite common to associate different non-zero values of an error code with specific errors. Error codes suffered from two major problems: No one was forced to actually check the value of returned error codes. Changes (additions, deletions, and modifications) in the meanings of the special values assigned to error codes were not automatically passed on to interested parties. Tracking the effects of a changed error code value often consumed a significant amount of resources. To understand how exceptions directly address both of these issues, we first need to understand how exceptions typically work: Exceptions may be defined by the environment or by the user. When an exceptional (but not unforeseen) condition occurs, an appropriate exception is activated. (People use different terms to express the activation of an exception. The most common is raise. Less commonly, people use the terms throw or activate.) This activation may be automatic (controlled by the environment) or may be expressly requested by the designer of the object or application. Examples of exceptional conditions include trying to remove something from an empty container, directing an elevator on the top floor to go up, and attempting to cause a date to take on an invalid value like February 31, 1993. Once the exception is activated, normal application execution stops and control is transferred to a locally defined exception handler, if one is present. If no locally defined exception handler is present or if the exception handler is not equipped to handle the exception, the exception is propagated to the next higher level of the application. Exceptions cannot be ignored. An exception will continue to be sent to higher levels of the application until it is either turned off or the application ceases to function. An exception handler checks to see what type of exception has been activated. If the exception is one that the handler recognizes, a specific set of actions is taken. Executing a set of actions in response to an exception is known as handling the exception. Handling an exception deactivates the exception; the exception will not be propagated any further. Unlike error codes, exceptions cannot be ignored. Once an exception has been activated, it demands attention. In object-oriented systems, exceptions are placed in the public interfaces of objects. Changes in the public interfaces of objects very often require an automatic rechecking of all other objects that invoke operations in the changed objects. Thus, changes in exceptions result in at least a partially automated propagation of change information. Object Coupling and Object Cohesion Engineers have known for centuries that the less any one part of a system knows about any other part of that same system, the better the overall system. Systems whose components are highly independent of each other are easier to fix and enhance than systems where there are strong interdependencies among some or all of the components. Highly independent system components are possible when there is minimal coupling among the components, and each component is highly cohesive. Coupling is a measure of the strength of the connection between any two system components. The more any one component knows about another component, the tighter (worse) the coupling is between those two components. Cohesion is a measure of how logically related the parts of an individual component are to each o

The Black Cat and The Tell-Tale Heart :: essays research papers

'The Black Cat'; and 'The Tell-Tale Heart' Poe was a literary master with the emotions of his readers. He could make a reader feel anything he wanted to with just a few sentences. Through the stories 'The Black Cat'; and 'The Tell-Tale Heart';, he takes the reader through the emotions of his characters using writing methods that draw the reader in. His use of sentence structure and writing style allows the reader to become intimate with the character. Poe knew how the get a reader deep into the story; he could make them believe as thought they went through the deeds with the character. It is how Poe accomplishes this feat that is very interesting topic. Poe makes his characters more human than human. This allows many readers to become interested simply because they can identify with how the characters feel. Poe uses very basic human emotions like fear, hatred, anxiety and guilt to draw in audience's interests. The main character in The Tell-Tale Heart had an unnatural hatred for a physical characteristic on a friend. He 'thinks it was his eye! yes, it was [that]! One of his eyes resembled that of a vulture, a pale blue eye, with a film over it';, his blood ran cold whenever it fell upon him (106). This is something many people can identify with as many have experienced a hatred for a physical characteristic on someone they know. Just as the character did not understand the hatred but just saw this body part, far out of the control of the old man, as something to be vanquished. The simple emotions of fear and hatred put forth to the reader come through clearly Poe's writing technique. In the Black Cat, Poe's mechanism for the reader becoming intimate with the protagonist is the use of an alcohol driven rage. Many readers now and in Poe's