Overriding Vs Redefinition

[Sathya Shanmugam]

I am quite confused with redefinition. In KB book it mentioned that overrriding is different from Redefinition.

Any example with explanation would greatly appreciated..

[Chandra Bhatt]

I am quite confused with redefinition. In KB book it mentioned that overrriding is different from Redefinition.

When you override a method you open the door of having polymorphic behavior.
That is calling subclass version of the method using parent class reference.

So far redefing is concerned, there is nothing like polymorphism. Redefining takes place in case of static methods because static methods can't be overridden (they are class specific things).

Look at the following example:

    
 
class A {
    static void meth1() {
        System.out.println("meth1() of the class A");
    }
 
    public void meth2() {
         System.out.println("meth2() of class A");
    }
 
}
 
class B extends A {
    static void meth1() {
         System.out.println("meth1() of class B");
    }
 
     public void meth2() {
         System.out.println("meth2() of class B");
     }
 
public static void main(String... args) {
     A a1 = new A();
     a1.meth1();
     a1.meth2();
 
     A a2 = new B();
     a2.meth1();
     a2.meth2();
     
     B b1 = new B();
     b1.meth1();
     b1.meth2();
}
}
 
output:
meth1() of class A
meth2() of class A
 
meth1() of class A
meth2() of class B
 
meth1() of class B
meth2() of class B

You can see easily, while redefining a method is different, it simply hides the parent class method. While overriding a method gives you avail run time method invocation decision on behalf of what type of object your reference variable is holding instead of the type of reference variable(that is taking place when calling static methods).

Hope you got the concept!

Thanks and Regards,
cmbhatt

[megha joshi]

Can we use covariant returns when re-defining?

[Chandra Bhatt]

Originally posted by Megha Joshi

Can we use covariant returns when re-defining?

Hi Megha,

While redefining a method, you can change the method return type. The actual meaning of covariant return is availed when we override a method so that run time polymorphism is assured.

Look at the code example below:

   
package covariant;
 
/**
 *
 * @author cmbhatt
 */
 
class Animal1 {
    Animal meth() {
        return new Animal();
    }
    
    public String toString() {
        return "It's Animal";
    }
    
    static Object method2() {
        return "method2() of Animal";
    }        
}
 
class Dog1  extends Animal1 {    
    Dog meth() {
        return new Dog();
    }        
    
    static String method2() {
        return "method2() of Dog";
    }
    public String toString() {
        return "It's Dog";
    }
}
 
public class DemoCovariant { 
    
    /** Creates a new instance of DemoCovariant */
    public DemoCovariant() {
    }
 
    public static void main(String... args){
        Animal1 ani = new Dog1();
        System.out.println(ani.meth()); 
        System.out.println(ani.method2());
        
        Dog1 dog = new Dog1();
        System.out.println(dog.meth());
        System.out.println(dog.method2());
    }        
}
 
Output:
It's Dog
method2() of Animal
It's Dog
method2() of Dog
 

You may comprehend this!

Thanks and Regards,
cmbhatt

[Sathya Shanmugam]

thanks chan, now I got clear picture