状态模式

定义

当一个对象内在状态改变时允许其改变行为，这个对象看起来像改变了其类

代码

抽象状态

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public abstract class State {
    protected Context context;

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

    public abstract void handle1();
    public abstract void handle2();

}

具体状态

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public class ConcreteState1 extends State {

    @Override
    public void handle1() {
        System.out.println("concrete state 1 handle1");
    }

    @Override
    public void handle2() {
        super.context.setCurrentState(Context.STATE2);
        super.context.handle2();
    }
}
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public class ConcreteState2 extends State {

    @Override
    public void handle1() {
       super.context.setCurrentState(Context.STATE1);
       super.context.handle1();
    }

    @Override
    public void handle2() {
        System.out.println("concrete state 2 handle2");
    }
}

环境角色

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public class Context {
    public final static State STATE1 = new ConcreteState1();
    public final static State STATE2 = new ConcreteState2();

    private State currentState;

    public State getCurrentState() {
        return currentState;
    }

    public void setCurrentState(State currentState) {
        this.currentState = currentState;
        //切换状态
        this.currentState.setContext(this);
    }

    public void handle1(){
        this.currentState.handle1();
    }

    public void handle2(){
        this.currentState.handle2();
    }

}

测试

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public class ContextTest {

    @Test
    public void testState(){
        Context context = new Context();
        context.setCurrentState(new ConcreteState1());
        context.handle1();
        context.handle2();
    }
}