Java Tutorial/Design Pattern/State Pattern

Simple demonstration of the State pattern.

interface State {
  void operation1();
  void operation2();
  void operation3();
}
class ServiceProvider {
  private State state;
  public ServiceProvider(State state) {
    this.state = state;
  }
  public void changeState(State newState) {
    state = newState;
  }
  public void service1() {
    state.operation1();
    state.operation3();
  }
  public void service2() {
    state.operation1();
    state.operation2();
  }
  public void service3() {
    state.operation3();
    state.operation2();
  }
}
class Implementation1 implements State {
  public void operation1() {
    System.out.println("Implementation1.operation1()");
  }
  public void operation2() {
    System.out.println("Implementation1.operation2()");
  }
  public void operation3() {
    System.out.println("Implementation1.operation3()");
  }
}
class Implementation2 implements State {
  public void operation1() {
    System.out.println("Implementation2.operation1()");
  }
  public void operation2() {
    System.out.println("Implementation2.operation2()");
  }
  public void operation3() {
    System.out.println("Implementation2.operation3()");
  }
}
public class StateDemo {
  static void run(ServiceProvider sp) {
  }
  public static void main(String args[]) {
    ServiceProvider sp = new ServiceProvider(new Implementation1());
    sp.service1();
    sp.service2();
    sp.service3();
    sp.changeState(new Implementation2());
    sp.service1();
    sp.service2();
    sp.service3();
  }
}

State: changing object behavior

interface Animal {
  String talk();
}
class Frog implements Animal {
  public String talk() {
    return "ggg!";
  }
}
class Cat implements Animal {
  public String talk() {
    return "miao";
  }
}
class Creature {
  private Animal state = new Frog();
  public void greet() {
    System.out.println(state.talk());
  }
  public void toCat() {
    state = new Cat();
  }
}
public class MainClass {
  public static void main(String args[]) {
    Creature creature = new Creature();
    creature.greet();
    creature.toCat();
    creature.greet();
  }
}