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。