16921 l7 inheritance

8/11/2019 16921 L7 Inheritance

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Modern Programming Tools And

Techniques-I Inheritance

ByArvind Kumar

Asst. Professor, LPU


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Inheritance Inheritance allows us to use one class by another class.

A class that is derived from another class is calleda subclass (also a derived class , extended class , or child class ).

The class from which the subclass is derived is called

a superclass (also a base class or a parent class ).

Classes can be derived from classes that are derived fromclasses that are derived from classes, and so on, and ultimatelyderived from the topmost class called Object.


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Excepting Object, which has no superclass, every class hasone and only one direct superclass (single inheritance). In the

absence of any other explicit superclass, every class isimplicitly a subclass of Object.

A subclass inherits all the members (fields, methods, and

nested classes) from its superclass. Constructors are notmembers, so they are not inherited by subclasses, but theconstructor of the superclass can be invoked from the subclass.

A class can inherits only one superclass at a time. But a classcan have several sub classes.


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Simple Inheritance

When a subclass is derived simply from it's parentclass then this mechanism is known as simpleinheritance.

In case of simple inheritance there is only a sub classand it's parent class. It is also called single inheritanceor one level inheritance.


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A subclass includes all of the members of its superclass , itcannot access those members of the superclass that have beendeclared as private .

To inherit a class, you simply incorporate the definition of oneclass into another by using the extends keyword.

Syntax:class sub_class_name extends super_class{

//body of the sub class. }


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class A{ int i, j;

void showij()

{System.out.println("i and j: " + i + " " + j);

} }class B extends A{int k;void showk()

{ System.out.println("k: " + k); }void sum()

{ System.out.println("i+j+k: " + (i+j+k)); }

public static void main (String args[]){B r=new B();r.sum();}

}


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Multilevel Inheritance

It is the enhancement of the concept of inheritance. When asubclass is derived from a derived class then this mechanism isknown as the multilevel inheritance.

The derived class is called the subclass or child class for it's parent class and this parent class works as the child class forit's just above (parent) class.

Multilevel inheritance can go up to any number of level .


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class A{ int x; int y;

int get( int p, int q){ x=p; y=q; return (0); }void Show(){ System.out.println(x); }

}class B extends A

{ void Showb(){ System.out.println("B"); }}class C extends B{ void display(){ System.out.println("C"); }

public static void main(String args[]){ B a = new B();

a.get(5,6);a.Show();

}}


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Multiple Inheritance

The mechanism of inheriting the features of more than one base class into a single class is known as multiple inheritance.

Java does not support multiple inheritance but the multiple

inheritance can be achieved by using the interface.

In Java Multiple Inheritance can be achieved through use ofInterfaces by implementing more than one interfaces in a class.


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Method Overloading

Method overloading means having two or more methods withthe same name but different signatures in the same scope.

It allows creating several methods with the same name which

differ from each other in the type of the input and the output ofthe method.

It is simply defined as the ability of one method to perform

different tasks.


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Exampleclass Area11

{void area(int a)

{int area = a*a;System.out.println("area of square is:" + area);

}void area (int a, int b)

{int area = a*b;

System.out.println("area of rectangle is:" + area);}

}


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class OverloadDemo{

public static void main (String arr[]){Area11 ar= new Area11();ar.area(10);ar.area(10,5);

}}


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Method Overriding Method overriding means having a different implementation

of the same method in the inherited class .

These two methods would have the same signature, but

different implementation.

One of these would exist in the base class and another in thederived class . These cannot exist in the same class.


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class Superclass{ public void printMethod()

{System.out.println("Printed in Superclass.");

}}class Subclass extends Superclass{ // overrides printMethod in Superclass

public void printMethod(){

System.out.println("Printed in Subclass");}

public static void main(String[] args){ Subclass s = new Subclass();

s.printMethod();}}


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class Override{ public void display()

{System.out.println("Hello...This is superclass display");}

}

class Override1 extends Override{ public void display()

{System.out.println("Hi...This is overriden method in

subclass");}

}


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class OverrideDemo{

public static void main(String arr[]){

Override o = new Override();o.display();

Override1 o1 = new Override1();o1.display();

}

}


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Dynamic Method Dispatch

Dynamic method dispatch is the mechanism by whicha call to an overridden method is resolved at run time,rather than compile time.

Dynamic method dispatch is important because this ishow Java implements run-time polymorphism.


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class A {void callme() {

System.out.println("Inside A's callme method");}

}

class B extends A {

void callme() {System.out.println("Inside B's callme method");}

}

class C extends A {void callme() {

System.out.println("Inside C's callme method");}

}


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class Dispatch { public static void main(String args[]) {

A a = new A(); // object of type AB b = new B(); // object of type BC c = new C(); // object of type CA r; // obtain a reference of type A

r = a; // r refers to an A objectr.callme(); // calls A's version of callme

r = b; // r refers to a B objectr.callme(); // calls B's version of callme

r = c; // r refers to a C objectr.callme(); // calls C's version of callme}

}


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class Superclass{ public void printMethod()



public void printMethod(){

super.printMethod();System.out.println("Printed in Subclass");

} public static void main(String[] args){ Subclass s = new Subclass();

s.printMethod();}}


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Using super A subclass can call a constructor defined by its

superclass by use of the following form of super:super( arg-list);

Here, arg-list specifies any arguments needed by theconstructor in the superclass.

super( ) must always be the first statement executedinside a subclass constructor.


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class Superclass{ Superclass ()



Subclass (){

super();System.out.println("Printed in Subclass");

} public static void main(String[] args){ Subclass s = new Subclass();}}


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Private Members in a Superclass A subclass does not inherit the private members of its parent

class. However, if the superclass has public or protectedmethods for accessing its private fields, these can also be used

by the subclass .

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 ofsuperclass, specify call to public method of superclass:MethodName(parameter list)


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Final Classes You can declare some or all of a class's methods final . You use

the final keyword in a method declaration to indicate that themethod cannot be overridden by subclasses.

A final class cannot be subclassed. This is done for reasons ofsecurity and efficiency. Accordingly, many of the Javastandard library classes are final.

A final class implicitly has all the methods as final, but notnecessarily the data members.

The Object class does this a number of its methods are final.Syntax:public final class MyFinalClass {...}
http://en.wikipedia.org/wiki/Class_(computer_science)http://en.wikipedia.org/wiki/Class_(computer_science)


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public final class FinalClass{Void meth(){System.out.println("Printed in FinalClass.");}}

public class SubClass extends FinalClass{

public static void main(String[] args){

System.out.println("Printed in SubClass."); }

}


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Final Methods

A final method can't be overridden by subclasses.This is used to prevent unexpected behavior from asubclass altering a method that may be crucial to thefunction or consistency of the class.

Examplepublic class MyClass{

public final void myFinalMethod() {...}}
http://en.wikipedia.org/wiki/Method_(computer_science)http://en.wikipedia.org/wiki/Method_overridinghttp://en.wikipedia.org/wiki/Method_overridinghttp://en.wikipedia.org/wiki/Method_(computer_science)


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Abstract Methods

A method that has only the heading with no body.

Must be declared abstract.

public abstract void print(); public abstract object larger(object, object);abstract void insert( int insertItem);


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Abstract Classes

A class that is declared with the reserved word abstract inits heading.

An abstract class can contain instance variables,constructors, finalizers, and non-abstract methods.

An abstract class can contain abstract methods. If a class contains an abstract method, the class must be

declared abstract. You can instantiate an object of a subclass of an abstract

class, but only if the subclass gives the definitions of all

the abstract methods of the superclass.


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Abstract Class Example public abstract class AbstractClassExample{

protected int x; public abstract void print();

public void setX( int a){

x = a;}

public AbstractClassExample(){

x = 0;}

}


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abstract class Shape{ public static float pi = 3.142f; protected float height; protected floatwidth; abstract float area() ;}

class Square extends Shape{Square(float h, float w){height = h; width = w;}final float area(){return height * width;}}class FinalMethodDemo{

public static void main(String args[]){

Square sObj = new Square(5,5);

System.out.println("Area of square : " + sObj.area());}}


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class A{void get()

{ System.out.println("A"); }}class B extends A{void get()

{ System.out.println("B"); }}class C{public static void main(String ar[]){A obj= new B();

obj.get();}}

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16921 l7 inheritance

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