一句话总结

状态和行为

内容

状态模式的核心是状态和行为的绑定,不同状态对应不同的行为。

场景

订单状态的变化;电梯的变化

类图

代码示例

//环境类
public class Context {
    public static final State STATE_A = new ConcreteStateA();
    public static final State STATE_B = new ConcreteStateB();
    // 默认状态A
    private State currentState = STATE_A;
    {
        STATE_A.setContext(this);
        STATE_B.setContext(this);
    }

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

    public State getState() {
        return this.currentState;
    }

    public void handle() {
        this.currentState.handle();
    }
}
// 抽象状态：State
public abstract class State {
    protected Context context;

    public void setContext(Context context) {
        this.context = context;
    }

    public abstract void handle();
}
//具体状态类
public class ConcreteStateA extends State {
    @Override
    public void handle() {
        System.out.println("StateA do action");
        // A状态完成后自动切换到B状态
        this.context.setState(Context.STATE_B);
        this.context.getState().handle();
    }
}
//具体状态类
public class ConcreteStateB extends State {
    @Override
    public void handle() {
        System.out.println("StateB do action");
    }
}
public class Test {
    public static void main(String[] args) {
        Context context = new Context();
        context.setState(new ConcreteStateA());
        context.handle();
    }
}

源码

无