状态模式

状态模式：允许在其内部状态变化的时候改变他的行为。可以理解为对象的行为其实是由他的状态来驱动的。

package com.jerry.design.state;



	// 测试类
public class Test {

	public static void main(String[] args) {
		State state = new StateA();
	    StateManager controller = new StateManager(state);
	    for (int i = 0; i < 10; i++) {
	      state = controller.nextState();
	      System.out.print(state);
	      if(state == null) break;
	      System.out.print("->");
	      controller.nextStep();
		
	}
}
}
 interface State {
	
 public void lastState(StateManager c);
 
 public void nextState(StateManager c);
 
}

class StateA implements State {
	
 public void lastState(StateManager c) {
   c.setState(new StateC());
 }
 
 public void nextState(StateManager c) {
   c.setState(new StateB());
 }
 
 @Override
 public String toString() {
	   return "i am StateA!";
 }
}

class StateB implements State {
	
	 public void lastState(StateManager c) {
	   c.setState(new StateA());
	 }
	 
	 public void nextState(StateManager c) {
	   c.setState(new StateC());
	 }
	 
	 @Override
	 public String toString() {
		   return "i am StateB!";
	 }
}

class StateC implements State {
	
	 public void lastState(StateManager c) {
	   c.setState(new StateB());
	 }
	 
	 public void nextState(StateManager c) {
	   c.setState(new StateA());
	 }
	 
	 @Override
	 public String toString() {
	   return "i am StateC!";
	 }
}

class StateManager {
	
	 private State state;
	 
	 private StateManager(){}

	 public StateManager(State initState){
	   this.state = initState;
	 }

	 public void setState(State state) {
	   this.state = state;
	 }

	 public void nextStep(){
	   if(this.state != null)
	     this.state.nextState(this);
	 }

	 public void lastStep(){
	   if(this.state != null)
	     this.state.lastState(this);
	 }

	 public State nextState(){
	   return this.state;
	 }
	}

这个例子的难点其实是这个状态管理器，其中用一个State对象维护了当前状态和下一个状态，通过设置这个state对象的不同状态来获得不同的state的方法调用。