extent and implementation of class in JAVA

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extent and implementation of class in JAVA

Post  Skyfall on Mon Jul 15, 2013 10:19 pm

extends is for extending a class.

implements is for implementing an interface

The difference between an interface and a regular class is that in an interface you can only specify methods.

Also java doesn't support multiple inheritance for classes. This is solved by using multiple interfaces

public interface Inter{
   public void do();
   public String doThis(int number);

public class sub implements Inter{
    public void do(){
      //specify what must happen

    public String doThis(int number){
      //specfiy what must happen

now extending a class

public class SuperClass{
   public int getNb(){
        //specify what must happen
       return 1;

    public int getNb2(){
        //specify what must happen
       return 2;

public class SubClass extends SuperClass{
     //you can override the implementation
     public int getNb2(){
       return 3;

in this case

 Subclass s = new SubClass();
 s.getNb(); //returns 1
 s.getNb2(); //returns 3

 SuperClass sup = new SuperClass();
 sup.getNb(); //returns 1
 sup.getNb2(); //returns 2

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