状态模式 - Demo （可切换代码块）

public class Status {

    public static void main(String[] args) {
        Context context = new Context(new ConcreteStateA());
        context.Request();
        context.Request();
        context.Request();
        context.Request();
    }
}
//抽象的状态类
abstract class State{
    public String stateName;
    public abstract void Handle(Context context);
}
//具体的状态A
class ConcreteStateA extends State{

    public ConcreteStateA() {
        stateName = "状态A";
    }
    
    @Override
    //处理方法
    public void Handle(Context context) {
        context.setState(new ConcreteStateB());
        
    }
    
}
//具体的状态B
class ConcreteStateB extends State{
    public ConcreteStateB() {
        stateName = "状态B";
    }

    @Override
    public void Handle(Context context) {
        context.setState(new ConcreteStateA());
    }
    
}
//Context类
class Context{
    private State state;
    public Context (State state) {
        this.state = state;
    }
    //设置状态
    public void setState(State state) {
        System.out.println("当前状态为 :"+this.state.stateName);
        this.state = state;
        System.out.println("状态变更为："+this.state.stateName);
        System.out.println("******************");
    }
    public void Request() {
        state.Handle(this);
    }
}

输出为： 

　　当前状态为 :状态A
　　状态变更为：状态B
　　******************
　　当前状态为 :状态B
　　状态变更为：状态A
　　******************
　　当前状态为 :状态A
　　状态变更为：状态B
　　******************
　　当前状态为 :状态B
　　状态变更为：状态A
　　******************