[设计模式]之十二:状态模式

//声明一个状态接口，统一通过HandleState处理状态
interface IState {
	public void HandleState(StateManager manager);
}
//具体状态类 这里不同状态类可以做一些与这些状态相关的简单处理逻辑
public class ConcreteStateA implements IState {

	@Override
	public void HandleState(StateManager manager) {
		if (someState) {
			...
		} else {
			...
		}
      // 当前stateA 改变为 stateB
		manager.setState(new ConcreteStateB());
	}

}

public class ConcreteStateB implements IState {

	@Override
	public void HandleState(StateManager manager) {
      // 当前stateB 改变为 stateA
		manager.setState(new ConcreteStateA());
	}
	
}
//状态管理类 私有一个 state对象，通过开放外部接口updateState对状态更新
public class StateManager {
	private IState state;
	
	public IState getState() {
		return state;
	}

	public void setState(IState state) {
		System.out.println("Set new state " + state.getClass().getName());
		this.state = state;
	}

	public StateManager(IState state) {
		System.out.println("Current state is " + state.getClass().getName());
		this.state = state;
	}
	
	public void updateState() {
		state.HandleState(this);
	}
	
}
//客户代码
public static void main(String[] args) {

  //初始化一个状态管理对象，给他一个初始状态，随后的状态切换由各自具体state类处理，上层只需要在某些条件下进行触发更新状态操作即可
	StateManager manager = new StateManager(new ConcreteStateA());
	
	manager.updateState();
	manager.updateState();
	manager.updateState();
	
}
//输出
Current state is ConcreteStateA
Set new state ConcreteStateB
Set new state ConcreteStateA
Set new state ConcreteStateB