该如何实践State模式

• Z时代
• 2024-01-10
• 分类：IT

State模式将对象行为的变化封装成具有统一接口的状态，它与Strategy模式的区别在于任何状态的改变都是定义好的，即“改变行为”的动作由自己来做。

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下面是自动门的状态图，它描述了“开”与“关”两个状态之间的变化条件。

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抽象状态DoorState提供open()和close()两个方法，

package com.zj.doorstate;   publicinterface DoorState {     void open();       void close(); }

Context为AutoDoor，它关联一个DoorState state。

package com.zj.doorstate;   publicclass AutoDoor {     private DoorState state;     private DoorState open = new Open(this);     private DoorState close = new Close(this);       public AutoDoor() {        this.state = open;     }       publicvoid setSate(DoorState state) {        this.state = state;     }       public DoorState getOpenState() {        returnopen;     }       public DoorState getCloseState() {        returnclose;     }       publicvoid open() {        state.open();     }       publicvoid close() {        state.close();     } }

ConcreteState有两个。

     状态Open

package com.zj.doorstate;   publicclass Open implements DoorState {     private AutoDoor door;       public Open(AutoDoor door) {        this.door = door;     }       publicvoid close() {        System.out.println("O.K. Door closed.");        door.setSate(door.getCloseState());     }       publicvoid open() {        System.out.println("Door already opened.");     } }

状态Close

package com.zj.doorstate;   publicclass Close implements DoorState {     private AutoDoor door;       public Close(AutoDoor door) {        this.door = door;     }       publicvoid close() {        System.out.println("Door already closed.");     }       publicvoid open() {        System.out.println("O.K. Door opened.");        door.setSate(door.getOpenState());     } }

由两个具体状态类可知，具体状态之间的转换由它们自身定义。

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