![What Is and What Isn’t an Object
• an object is any of the following:
• A tangible and/or visible thing
• Something that may be comprehended intellectually
• Something toward which thought or action is directed
• Jacobson et al. define control objects as “the ones that unite
courses of events and thus will carry on communication with
other objects” [62].
• This leads us to the more refined definition of Smith and Tockey,
who suggest that “an object represents an individual,
identifiable item, unit, or entity, either real or abstract, with a
well-defined role in the problem domain”](https://image.slidesharecdn.com/lectureno-250812060027-33d04c0f/85/Object-Oriented-Programming-Concepts-Def-3-320.jpg)
Object Oriented Programming Concepts Def
- 2. Benefits of the Object Model • First, the use of the object model helps us to exploit the expressive power of object-based and object-oriented programming languages, using the class and object as basic building blocks. • Second, the use of the object model encourages the reuse not only of software but of entire designs, leading to the creation of reusable application frameworks • Third, the use of the object model produces systems that are built on stable intermediate forms, which are more resilient to change.
- 3. What Is and What Isn’t an Object • an object is any of the following: • A tangible and/or visible thing • Something that may be comprehended intellectually • Something toward which thought or action is directed • Jacobson et al. define control objects as “the ones that unite courses of events and thus will carry on communication with other objects” [62]. • This leads us to the more refined definition of Smith and Tockey, who suggest that “an object represents an individual, identifiable item, unit, or entity, either real or abstract, with a well-defined role in the problem domain”
- 4. • Some objects may have crisp conceptual boundaries yet represent intangible events or processes. • For example, a chemical process in a manufacturing plant may be treated as an object because it has a crisp conceptual boundary, interacts with certain other objects through a well-ordered collection of operations that unfolds over time, and exhibits a well-defined behavior.
- 5. An object is an entity that has state, behaviour, and identity. The structure and behaviour of similar objects are defined in their common class. The terms instance and object are interchangeable.
- 6. State The state of an object encompasses all of the (usually static) properties of the object plus the current (usually dynamic) values of each of these properties. Employee Class with Attributes Employee Objects Tom and Kaitlyn
- 7. Behaviour • Behaviour is how an object acts and reacts, in terms of its state changes and message passing. • In other words, the behaviour of an object represents its outwardly visible activity. • An operation is some action that one object performs on another in order to elicit a reaction. • For example, a client might invoke the operations append and pop to grow and shrink a queue object, respectively. • A client might also invoke the operation length, which returns a value denoting the size of the queue object but does not alter the state of the queue itself. • Message passing is one part of the equation that defines the behaviour of an object; our definition for behaviour also notes that the state of an object affects its behaviour as well.
- 8. Operations • An operation denotes a service that a class offers to its clients. In practice, we have found that a client typically performs five kinds of operations on an object. • The three most common kinds of operations are the following: • Modifier/ Mutators : an operation that alters the state of an object • Selector/ Accessors : an operation that accesses the state of an object but does not alter the state • Iterator: an operation that permits all parts of an object to be accessed in some well-defined order
- 9. •Two other kinds of operations are common; they represent the infrastructure necessary to create and destroy instances of a class. • Constructor: an operation that creates an object and/or initializes its state • Destructor: an operation that frees the state of an object and/or destroys the object itself
- 10. Categories of methods • accessor: A method that lets clients examine object state. • Examples: getX(), distanceFromOrigin • often has a non-void return type • mutator: A method that modifies an object's state. • Examples: setLocation, translate • helper: Assists some other method in performing its task. • often declared as private so outside clients cannot call it
- 11. Identity • Khoshafian and Copeland offer the following definition for identity: “Identity is that property of an object which distinguishes it from all other objects” • “most programming and database languages use variable names to distinguish temporary objects, mixing addressability and identity. Most database systems use identifier keys to distinguish persistent objects, mixing data value and identity.” • The failure to recognize the difference between the name of an object and the object itself is the source of many kinds of errors in object oriented programming.
- 12. The Nature of a Class • Webster’s Third New International Dictionary defines a class as “a group, set, or kind marked by common attributes or a common attribute; a group division, distinction, or rating based on quality, degree of competence, or condition” • In the context of object-oriented analysis and design, we define a class as follows: • A class is a set of objects that share a common structure, common behaviour, and common semantics. • A single object is simply an instance of a class.
- 14. What isn’t a class? An object is not a class. Objects that share no common structure and behaviour cannot be grouped in a class because, by definition, they are unrelated except by their general nature as objects.
- 15. Interface and Implementation • The interface of a class provides its outside view and therefore emphasizes the abstraction while hiding its structure and the secrets of its behaviour. • This interface primarily consists of the declarations of all the operations applicable to instances of this class, but it may also include the declaration of other classes, constants, variables, and exceptions as needed to complete the abstraction. • By contrast, the implementation of a class is its inside view, which encompasses the secrets of its behaviour. • The implementation of a class primarily consists of the implementation of all of the operations defined in the interface of the class.
- 16. Summary •Abstraction • Shows only the essential attributes and hide unnecessary details from the user. • Purpose : Hide the complexity from the user
- 17. Class •Interface • The “visible” part of the class that the program • Can interact with •Implementation • The internal part of the class with the code that performs the functionality
- 19. 23 Reference • Object-Oriented Analysis and Design with Applications, Third Edition, Grady Booch, Robert A. Maksimchuk, Michael W. Engle, Bobbi J. Young, Ph.D., Jim Conallen,Kelli A. Houston