UT Dallas CS 4337 - #Sebesta ch12 oop - shorter to use (53 pages)

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#Sebesta ch12 oop - shorter to use



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#Sebesta ch12 oop - shorter to use

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Pages:
53
School:
University of Texas at Dallas
Course:
Cs 4337 - Organization of Programming Languages
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Chapter 12 Support for Object Oriented Programming Chapter 12 Topics Introduction Object Oriented Programming Design Issues for Object Oriented Languages Support for Object Oriented Programming in C Support for Object Oriented Programming in Java Implementation of Object Oriented Constructs Copyright 2012 Addison Wesley All rights reserved 1 2 Introduction Many object oriented programming OOP languages Some support procedural and data oriented programming e g Ada 95 and C Some support functional program e g CLOS Newer languages do not support other paradigms but use their imperative structures e g Java and C Some are pure OOP language e g Smalltalk Ruby Some functional languages support OOP but they are not discussed in this chapter Copyright 2012 Addison Wesley All rights reserved 1 3 Object Oriented Programming Three major language features Abstract data types Chapter 11 Inheritance Inheritance is the central theme in OOP and languages that support it Polymorphism Copyright 2012 Addison Wesley All rights reserved 1 4 Inheritance Productivity increases can come from reuse ADTs are difficult to reuse always need changes All ADTs are independent and at the same level Inheritance allows new classes defined in terms of existing ones i e by allowing them to inherit common parts Inheritance addresses both of the above concerns reuse ADTs after minor changes and define classes in a hierarchy Copyright 2012 Addison Wesley All rights reserved 1 5 Object Oriented Concepts ADTs are usually called classes Class instances are called objects A class that inherits is a derived class or a subclass The class from which another class inherits is a parent class or superclass Subprograms that define operations on objects are called methods Copyright 2012 Addison Wesley All rights reserved 1 6 Object Oriented Concepts continued Calls to methods are called messages The entire collection of methods of an object is called its message protocol or message interface Messages have two parts a method name and the destination object In the simplest case a class inherits all of the entities of its parent Copyright 2012 Addison Wesley All rights reserved 1 7 Object Oriented Concepts continued Inheritance can be complicated by access controls to encapsulated entities A class can hide entities from its subclasses A class can hide entities from its clients A class can also hide entities for its clients while allowing its subclasses to see them Besides inheriting methods as is a class can modify an inherited method The new one overrides the inherited one The method in the parent is overriden Copyright 2012 Addison Wesley All rights reserved 1 8 Object Oriented Concepts continued Three ways a class can differ from its parent 1 The parent class can define some of its variables or methods to have private access which means they will not be visible in the subclass 2 The subclass can add variables and or methods to those inherited from the parent 3 The subclass can modify the behavior of one or more of its inherited methods Copyright 2012 Addison Wesley All rights reserved 1 9 Object Oriented Concepts continued There are two kinds of variables in a class Class variables one class Instance variables one object There are two kinds of methods in a class Class methods accept messages to the class Instance methods accept messages to objects Single vs Multiple Inheritance One disadvantage of inheritance for reuse Creates interdependencies among classes that complicate maintenance Copyright 2012 Addison Wesley All rights reserved 1 10 Dynamic Binding Polymorphic Variables A polymorphic variable can be defined in a class that is able to reference or point to objects of the class and objects of any of its descendants For the Overriding Methods When a class hierarchy includes classes that override methods and such methods are called through a polymorphic variable and the binding to the correct method will be dynamic These features allow software systems to be more easily extended during both development and maintenance Copyright 2012 Addison Wesley All rights reserved 1 11 Dynamic Binding Conce Abstract Class Virtual Method An abstract method is one that does not include a definition it only defines a protocol An abstract class is one that includes at least one virtual method An abstract class cannot be instantiated Copyright 2012 Addison Wesley All rights reserved 1 12 Design Issues for OOP Languages The Exclusivity of Objects pure OOP or not Are Subclasses Subtypes is a relationship Single vs Multiple Inheritance Object Allocation and Deallocation Dynamic vs Static Binding Nested Classes or not Initialization of Objects Copyright 2012 Addison Wesley All rights reserved 1 13 The Exclusivity of Objects Everything is an object Advantage elegance and purity Disadvantage slow operations on simple objects Add objects to a complete typing system Advantage fast operations on simple objects Disadvantage results in a confusing type system two kinds of entities Include an imperative style typing system for primitives but make everything else objects Advantage fast operations on simple objects and a relatively small typing system Disadvantage still some confusion because of the two type systems Copyright 2012 Addison Wesley All rights reserved 1 14 Are Subclasses Subtypes Does an is a relationship hold between a parent class object and an object of the subclass If a derived class is a parent class then objects of the derived class must behave the same as the parent class object A derived class is a subtype if it has an isa relationship with its parent class Subclass can only add variables and methods and override inherited methods in compatible ways Copyright 2012 Addison Wesley All rights reserved 1 15 Single and Multiple Inheritance Multiple inheritance allows a new class to inherit from two or more classes Disadvantages of multiple inheritance Language and implementation complexity in part due to name collisions Potential inefficiency dynamic binding costs more with multiple inheritance but not much Advantage Sometimes it is quite convenient and valuable Copyright 2012 Addison Wesley All rights reserved 1 16 Allocation and DeAllocation of Objects From where are objects allocated If they behave like the ADTs they can be allocated from anywhere Allocated from the run time stack Explicitly create on the heap via new If they are all heap dynamic references can be uniform thru a pointer or reference variable Simplifies assignment


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