delegation example regarding java context

Question

What is delegation in Java? Can anyone give me a proper example?

Answer 1

That's delegation - exactly like in the real world:

public interface Worker() {   public Result work(); }  public class Secretary() implements Worker {     public Result work() {      Result myResult = new Result();      return myResult;    }     }  public class Boss() implements Worker {     private Secretary secretary;     public Result work() {      if (secretary == null) {         // no secretary - nothing get's done         return null;      }      return secretary.work();    }     public void setSecretary(Secretary secretary) {        this.secretary = secretary;    } } 

(Added Worker interface to get closer to the Delegator pattern)

Answer 2

If you're referring to the delegation pattern, wikipedia has a great example, written in java.

I believe the longer example of the page above is the best one:

interface I {     void f();     void g(); }  class A implements I {     public void f() { System.out.println("A: doing f()"); }     public void g() { System.out.println("A: doing g()"); } }  class B implements I {     public void f() { System.out.println("B: doing f()"); }     public void g() { System.out.println("B: doing g()"); } }  class C implements I {     // delegation     I i = new A();      public void f() { i.f(); }     public void g() { i.g(); }      // normal attributes     void toA() { i = new A(); }     void toB() { i = new B(); } }   public class Main {     public static void main(String[] args) {         C c = new C();         c.f();     // output: A: doing f()         c.g();     // output: A: doing g()         c.toB();         c.f();     // output: B: doing f()         c.g();     // output: B: doing g()     } }