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This and Super Keywords

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instanceof java

Posts: 576
Nickname: instanceof
Registered: Jan, 2015

instanceof java is a java related one.
This and Super Keywords Posted: Mar 8, 2015 6:20 AM
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Original Post: This and Super Keywords
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  • this keyword used to store current object reference.
  • super keyword used to store super class reference in subclass object.

this keyword:

  • Predefined instance variable to hold current object reference.

It must used explicitly if non-static variable and local variable name is same.


  1. package com.instanceofjava;
  2.  
  3. public class ThisDemo {
  4.     int a, b;
  5.  
  6.  ThisDemo(int a, int b){
  7.  
  8.         a=a;
  9.         b=b;
  10.  }
  11.  
  12.     public static void main(String[] args){
  13.  
  14.         ThisDemo obj= new ThisDemo(1,2);
  15.         
  16.         System.out.println(obj.a);
  17.         System.out.println(obj.b);
  18. }
  19. }

Output:

  1. 0
  2. 0
  • Without this keyword if variable names are same we can not assign instance variables so this problem will solve by using this keyword

  1. package com.instanceofjava;
  2.  
  3. public class ThisDemo {
  4.     int a, b;
  5.  
  6.  ThisDemo(int a, int b){
  7.  
  8.         this.a=a;
  9.        this.b=b;
  10.  }
  11.  
  12.     public static void main(String[] args){
  13.  
  14.         ThisDemo obj= new ThisDemo(1,2);
  15.         
  16.         System.out.println(obj.a);
  17.         System.out.println(obj.b);
  18. }
  19. }

Output:

  1. 1
  2. 2

Used to invoke current class constructor:

  1. package com.instanceofjava;
  2.  
  3. public class ThisDemo {
  4.     int a, b;
  5.  
  6. ThisDemo(){
  7. System.out.println("Default constructor called");
  8. }

  10.  ThisDemo(int a, int b){
  11.        this();
  12.         this.a=a;
  13.        this.b=b;
  14.  }
  15.  
  16.     public static void main(String[] args){
  17.  
  18.         ThisDemo obj= new ThisDemo(1,2);
  19.         
  20.         System.out.println(obj.a);
  21.         System.out.println(obj.b);
  22. }
  23. }

Output:

  1. Default constructor called
  2. 1
  3. 2

Used to call current class method:

 

  1. package com.instanceofjava;
  2.  
  3. public class Sample{
  4.     int a, b;
  5.  

  7.  Sample(int a, int b){
  8.       
  9.        this.a=a;
  10.        this.b=b;
  11.  }
  12.  
  13. void show(){
  14.  
  15. System.out.println("Show() method called");
  16.    
  17. }
  18.  
  19. void print(){
  20.  
  21.     this.show();
  22.     System.out.println(obj.a);
  23.     System.out.println(obj.b);
  24.  
  25.  }
  26.     public static void main(String[] args){
  27.  
  28.         Sample obj= new Sample(1,2);
  29.         
  30.       
  31.         obj.print()
  32. }
  33. }

Output:

  1. Show() method called
  2. 1
  3. 2

super keyword:

  • Predefined instance variable used to hold super class object reference through sub class object.

Used to call super class constructor:



  1. package com.instanceofjava;
  2.  
  3. public class A{
  4.     int a, b;
  5.  
  6.  A(int a, int b){
  7.  
  8.         a=a;
  9.         b=b;
  10. System.out.println("super class constructor called");
  11.  
  12.  }
  13.  
  14. }


  1. package com.instanceofjava;
  2.  
  3. public class B extends A{
  4.     int a, b;
  5.  
  6.  A(int a, int b){
  7.     super(a,b);
  8.         a=a;
  9.         b=b;
  10. }
  11. public static void main(String[] args){
  12.  
  13.         B obj= new B(1,2);
  14.         
  15.     
  16. }
  17.  
  18.  }
  19.  
  20. }

Output:

  1. super class constructor called
  2. 1
  3. 2

Used to call super class methods from subclass:


  1. package com.instanceofjava;
  2.  
  3. public class A{
  4.     int a, b;
  5.  
  6.  A(int a, int b){
  7.  
  8.         a=a;
  9.         b=b;
  10. System.out.println("super class constructor called");
  11.  
  12.  }
  13.  
  14. void add(){
  15. System.out.println("super class method called");
  16. }
  17.  
  18. }


  1. package com.instanceofjava;
  2.  
  3. public class B extends A{
  4.     int a, b;
  5.  
  6.  A(int a, int b){
  7.     super(a,b);
  8.         a=a;
  9.       
  10. }
  11. void print(){ 
  12. super.add();
  13. System.out.println(this.a);
  14. System.out.println(this.b);
  15.  


  18. }
  19. public static void main(String[] args){
  20.  
  21.         B obj= new B(1,2);
  22.         
  23.        obj.print();
  24. }
  25.  
  26.  }
  27.  
  28. }

Output:

  1. super class method called
  2. 1
  3. 2

Read: This and Super Keywords

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