// patterns/StateDemo.java

// (c)2021 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.

// Basic demonstration of the State pattern.

class State {

private State implementation;

protected State() {}

public State(State imp) {

implementation = imp;

}

public void change(State newImp) {

implementation = newImp;

}

// Forward method calls to the implementation:

public void f() { implementation.f(); }

public void g() { implementation.g(); }

public void h() { implementation.h(); }

}

class Implementation1 extends State {

@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()");

}

}

class Implementation2 extends State {

@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()");

}

}

public class StateDemo {

static void test(State s) {

s.f();

s.g();

s.h();

}

public static void main(String[] args) {

State s = new State(new Implementation1());

test(s);

System.out.println("Changing implementation");

s.change(new Implementation2());

test(s);

}

}

/* Output:

Implementation1.f()

Implementation1.g()

Implementation1.h()

Changing implementation

Implementation2.f()

Implementation2.g()

Implementation2.h()

*/