// patterns/StateDemo.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Simple demonstration of the State pattern

interface StateBase {
 void f();
 void g();
 void h();
 void changeImp(StateBase newImp);
}

class State implements StateBase {
 private StateBase implementation;
 State(StateBase imp) {
 implementation = imp;
 }
 @Override
 public void changeImp(StateBase newImp) {
 implementation = newImp;
 }
 // Pass method calls to the implementation:
 @Override
 public void f() { implementation.f(); }
 @Override
 public void g() { implementation.g(); }
 @Override
 public void h() { implementation.h(); }
}

class Implementation1 implements StateBase {
 @Override
 public void f() {
 System.out.println("Implementation1.f()");
 }
 @Override
 public void g() {
 System.out.println("Implementation1.g()");
 }
 @Override
 public void h() {
 System.out.println("Implementation1.h()");
 }
 @Override
 public void changeImp(StateBase newImp) {}
}

class Implementation2 implements StateBase {
 @Override
 public void f() {
 System.out.println("Implementation2.f()");
 }
 @Override
 public void g() {
 System.out.println("Implementation2.g()");
 }
 @Override
 public void h() {
 System.out.println("Implementation2.h()");
 }
 @Override
 public void changeImp(StateBase newImp) {}
}

public class StateDemo {
 static void test(StateBase b) {
 b.f();
 b.g();
 b.h();
 }
 public static void main(String[] args) {
 StateBase b =
 new State(new Implementation1());
 test(b);
 b.changeImp(new Implementation2());
 test(b);
 }
}
/* Output:
Implementation1.f()
Implementation1.g()
Implementation1.h()
Implementation2.f()
Implementation2.g()
Implementation2.h()
*/