// patterns/StateDemo.java

// (c)2016 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://mindviewinc.com/Books/OnJava/ 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;

public 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()

*/