状态模式

状态模式：一个对象的内部状态发生改变会引起行为的改变，此种变化会引起类的变化

优点：避免过多的if-else语句，扩展性良好，有很强的封装性

 

标注类图： 

 模拟电梯状态行为：

电梯类：

public class Lift {
	public static final LiftOpenState OPEN_STATE = new LiftOpenState();
	public static final LiftCloseState CLOSE_STATE = new LiftCloseState();
	public static final LiftStopState STOP_STATE = new LiftStopState();
	public static final LiftRunState RUN_STATE = new LiftRunState();
	private LiftState currentState;
	
	public LiftState getCurrentState() {
		return currentState;
	}
	
	public void setCurrentState(LiftState currentState) {
		this.currentState = currentState;
		this.currentState.setLift(this);
	}
	
	public void open(){
		currentState.open();
	}
	
	public void close(){
		currentState.close();
	}
	
	public void stop(){
		currentState.stop();
	}
	
	public void run(){
		currentState.run();
	}
	
	
	
}

 抽象状态类：

public abstract class LiftState {
	
	protected Lift lift;
	
	public void setLift(Lift lift){
		this.lift = lift;
	}
	
	protected abstract void open();
	
	protected abstract void close();
	
	protected abstract void stop();
	
	protected abstract void run();
	
}

 具体状态类：

public class LiftOpenState extends LiftState{

	@Override
	public void open() {
		System.out.println("open");
	}

	@Override
	public void close() {
		super.lift.setCurrentState(Lift.CLOSE_STATE);
		super.lift.close();
	}

	@Override
	public void stop() {
		super.lift.setCurrentState(Lift.STOP_STATE);
		super.lift.stop();
	}

	@Override
	public void run() {
		super.lift.setCurrentState(Lift.RUN_STATE);
		super.lift.run();
	}


}

 

public class LiftCloseState extends LiftState{

	@Override
	public void open() {
		super.lift.setCurrentState(Lift.OPEN_STATE);
		super.lift.open();
	}

	@Override
	public void close() {
		System.out.println("close");
	}

	@Override
	public void stop() {
		super.lift.setCurrentState(Lift.STOP_STATE);
		super.lift.stop();
	}

	@Override
	public void run() {
		super.lift.setCurrentState(Lift.RUN_STATE);
		super.lift.run();
	}


}

 

public class LiftStopState extends LiftState{

	@Override
	public void open() {
		super.lift.setCurrentState(Lift.OPEN_STATE);
		super.lift.open();
	}

	@Override
	public void close() {
		super.lift.setCurrentState(Lift.CLOSE_STATE);
		super.lift.close();
	}

	@Override
	public void stop() {
		System.out.println("stop");
	}

	@Override
	public void run() {
		super.lift.setCurrentState(Lift.RUN_STATE);
		super.lift.run();
	}

}

 

public class LiftRunState extends LiftState{

	@Override
	public void open() {
		super.lift.setCurrentState(Lift.OPEN_STATE);
		super.lift.open();
	}

	@Override
	public void close() {
		super.lift.setCurrentState(Lift.CLOSE_STATE);
		super.lift.close();
	}

	@Override
	public void stop() {
		super.lift.setCurrentState(Lift.STOP_STATE);
		super.lift.stop();
	}

	@Override
	public void run() {
		System.out.println("run");
	}


}

 场景类： 

public class Client {

	public static void main(String[] args) {
		Lift lift = new Lift();
		lift.setCurrentState(Lift.OPEN_STATE);
		lift.stop();
	}
	
}

 

高层调用者不用关心状态的变化引起的行为的变化，而只是关注于具体的行为，具体的状态实现状态的过渡