structured programming good for programming in the small often doesn't scale up limitations...

Structured Programming

• Good for programming in the small

• Often doesn't scale up

• Limitations– Changes at top may affect lower-level

algorithms– Code reuse more difficult

Object Oriented Programming

• Emphasis on data

• Algorithms operations

• Features– Data abstraction– Encapsulation– Inheritance– Dynamic binding

OOP definition Java

Object self contained entity encapsulating data and operations on that data

Class object or class instance

Instance variable

maintains internal state of object

Private data member

Method public operations, only means by which the object's state can be inspected or modified by another object

Public member function

Message passing

method of communicating between objects

Function call to public member function

Relationships between classes

• Two classes are independent– Nothing in common

• Two classes are related by inheritance

• Two classes are related by composition

Inheritance hierarchy

Animal

Dogs Cat Horse

toy Sporting working

poodle labrador retriever greyhound German Shepherd

Inheritance

• Mechanism by which one class acquires the properties of another class

• Base class – class being inherited from• Derived class – the class that inherits• Is-a: every member of the derived class is also a

member of the base class– Derived class inherits all properties of base class

• allows us to create an object derived from another one, so that it may include some of the other's members plus its own

Inheritance ExamplesBase Class Derived Class

Student GraduateStudent

UndergraduateStudent

Shape Circle

Triangle

Rectangle

Loan CarLoan

HomeImprovementLoan

MortgageLoan

Employee Faculty

Staff

Account CheckingAccount

SavingsAccount

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Inheritance• “is-a” relationship• Single inheritance:

– Subclass is derived from one existing class (superclass)

• Multiple inheritance:– Subclass is derived from more than one

superclass– Not supported by Java– A class can only extend the definition of one

class

modifier(s) class ClassName extends BaseCassName modifier(s){ memberlist}

public class Circle extends Shape{ . . .}

superclasses and subclasses

• private members of superclass are not accessible to subclass

• Subclass can directly access public members of the superclass

• subclass can have more data or method members

• subclass class can redefine or override public methods of superclass

• All member variables and methods (unless overridden) of superclass are also members of the subclass

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UML Class Diagram: class Rectangle

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UML Class Diagram: class Box

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Defining Constructors of the Subclass

• Call to constructor of superclass: – Must be first statement– Specified by super parameter list

public Box(){ super(); height = 0;}

public Box(double l, double w, double h){ super(l, w); height = h;}

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class Boxpublic void setDimension(double l, double w, double h){ super.setDimension(l, w); if (h >= 0) height = h; else height = 0;}public double getHeight(){ return height;}

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class Boxpublic double area(){ return 2 * (getLength() * getWidth() + getLength() * height + getWidth() * height);}public double volume(){ return super.area()* height);}

public class SubClassSuperClassMethods{ public static void main(String[] args) { Rectangle myRectangle1 = new Rectangle(); //Line 1 Rectangle myRectangle2 = new Rectangle(8, 6); //Line 2

Box myBox1 = new Box(); //Line 3 Box myBox2 = new Box(10, 7, 3); //Line 4

System.out.println("Line 5: myRectangle1: " + myRectangle1); //Line 5

System.out.println("Line 6: Area of myRectangle1: "+ myRectangle1.area()); System.out.println("Line 7: myRectangle2: "+ myRectangle2); System.out.println("Line 8: Area of myRectangle2: "+ myRectangle2.area());

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Objects myRectangle and myBox

Rectangle myRectangle = new Rectangle(5, 3);Box myBox = new Box(6, 5, 4);

overloading

• Using the same name for operations on different types

• Method overloading allows several methods to share the same name but with a different set of parameters

• Each overloaded method performs a similar task

• Different parameters• Only considers parameters, not return type

Method overloading

public int square( int x )

{

return x * x;

}

public double square( double y )

{

return y * y;

}

Another common use of overloading is when defining constructors:

public Time( ) //default constructor

public Time( int hr, int min, int sec ) //general constructor

public Time( Time time ) //copy constructor

•Overloading occurs within a class.

Overriding

• similar to overloading

• except that it occurs between classes and

• each method has the same signature.

• A subclass can override a superclass method by redefining that method

• When the method is mentioned by name in the subclass, then the subclass version is automatically used.

overriding

Super class – Square, subclass – Cube

public double area( ) // Square class method

{

return getSide( ) * getSide( );

}

public double area( ) // Cube class overridden method

{

return super.area( ) * 6; // calls the Square version

}

Note: if super is omitted in the above call to area( ), then infinite recursion results.

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• To write a method’s definition of a subclass, specify a call to the public method of the superclass– If subclass overrides public method of

superclass, specify call to public method of superclass:

super.MethodName(parameter list)– If subclass does not override public method of

superclass, specify call to public method of superclass:

MethodName(parameter list)