作者：JAVA 发布时间：20080424 文章来源：

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

package com.zj.doorstate;   public class AutoDoor {     private DoorState state;     private DoorState open = new Open(this);     private DoorState close = new Close(this);       public AutoDoor() {        this.state = open;     }       public void setSate(DoorState state) {        this.state = state;     }       public DoorState getOpenState() {        return open;     }       public DoorState getCloseState() {        return close;     }       public void open() {        state.open();     }       public void close() {        state.close();     } }

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

package com.zj.doorstate;   public class Close implements DoorState {     private AutoDoor door;       public Close(AutoDoor door) {        this.door = door;     }       public void close() {        System.out.println("Door already closed.");     }       public void 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。