Object Oriented Programming Languages What are the benefits Systems more adaptive to change Appeals to human cognition Reuse Information hiding Encapsulation Gamma et al Design Patterns Methodologies for design and analysis Grady Booch Object Oriented Design Analysis CASE tools What is an OOPL No consensus Cardelli Wegner OO ADTs first class objects types inheriting attributes from a supertype Finkel OO encapsulation inheritance overloading Common features Classes Objects instantiation Single Inheritance redefinition Type inheritance Multiple inheritance Method overloading Dynamic lookup Deferred implementations Protection Other features Static typing Genericity Unit 8 Exception handling Garbage collection Design by contract Unit 9 Multiple polymorphism Reflection Meta object protocols Packages Class methods Iterators Operator overloading Classes A class is a software element that describes an ADT and its partial or total definition Meyer Can be viewed as a set of members or slots which can be Data attributes or fields Operations methods messages C Example class FixedIntStack int index arr public FixedIntStack int size index 0 arr new int size FixedIntStack delete arr void push int item arr index item int pop return arr index Instantiation Class instances are called objects and are first class entities Constructors run at instantiation time Arguments can be passed to instantiations Instantiation is usually handled by an operator In Eiffel new in C and Java Deallocation may call a destructor or finalization method Instantiation Example C FixedIntStack stack1 new FixedIntStack 10 FixedIntStack stack2 10 stack1 push 5 stack2 push 5 Java FixedIntStack myStack new FixedIntStack 10 myStack push 5 A trend objects PBR primitive types by value Inheritance Incremental program extension class Integer inherit Number Number is the parent of Integer Integer is the child or descendant of Number multiple inheritance class Mobile Home inherit Vehicle House Subclassing subtyping is a Subclassing code data sharing Subtyping type sharing substitutability a subtype may stand in for any parent type polymorphism void print Object ob Specialization is a implies subtyping and subclassing Java Example class Rectangle default extends Object float width height void set width float w width w void set height float h height h class Square extends Rectangle These are overridden redefined methods void set width float w super set width w super set height w void set height float w set width float w Method lookup binding Square s new Square s set width 12 Meaning is obvious Rectangle r s substitutability r set width 12 Dynamic lookup Square s method is called Static lookup Rectangle s method is called Java Dynamic Lookup C virtual keyword Liskov substitution principle Multiple Inheritance IOStream IStream OStream More from John Viega next Tuesday Protection A way to enforce encapsulation C no change by default private public protected members private public protected inheritance break the rules with friend class X protected Y private Z friend class Q public X private int datum Protection Eiffel No change by default secret non secret members selectively export operations to classes class MySecrets inherit GovtSecrets export NONE really big secret ANY common knowledge feature NSA CIA FBI big secret Secret end
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