java设计模式——State模式

1.静态主调函数

package com;

public class Test {

 /**
  * @param args
  */
 public static void main(String[] args) {
  // TODO Auto-generated method stub

  State state = new StateA();
  StateManager sm = new StateManager(state);
  for(int i=0;i<4;i++)
  {
   state = sm.nextState();
   System.out.print(":"+state);
   if(state == null)
   {
    System.out.print("-->");
   }
   sm.nextStep();
   
  }
  
 }

}

2.State接口类

package com;

public interface State {

 public void lastStep(StateManager s);
 public void nextStep(StateManager s);
}
3.状态管理类

package com;

public class StateManager {

 private State state;

 public StateManager(State initState) {
  super();
  // TODO Auto-generated constructor stub
  this.state = initState;
 }
 public void setState(State state)
 {
  this.state = state;
  
 }
  //下一步
   public void nextStep(){
     if(this.state != null)
       this.state.nextStep(this);
   }
 
   //上一步
   public void lastStep(){
     if(this.state != null)
       this.state.lastStep(this);
   }
 
   //返回下一个状态
   public State nextState(){
     return this.state;
   }

}
4.状态类

package com;

public class StateA implements State{

 @Override
 public void lastStep(StateManager s) {
  // TODO Auto-generated method stub
  s.setState(new StateC());
 }

 @Override
 public void nextStep(StateManager s) {
  // TODO Auto-generated method stub
  s.setState(new StateB());
 }

 @Override
 public String toString() {
  // TODO Auto-generated method stub
//  return super.toString();
  return "State A";
 }

// public void
}

package com;

public class StateB implements State{

 @Override
 public void lastStep(StateManager s) {
  // TODO Auto-generated method stub
  s.setState(new StateA());
 }

 @Override
 public void nextStep(StateManager s) {
  // TODO Auto-generated method stub
  s.setState(new StateC());
 }

 @Override
 public String toString() {
  // TODO Auto-generated method stub
//  return super.toString();
  return "State B";
 }

}

 

package com;

public class StateC implements State{

 @Override
 public void lastStep(StateManager s) {
  // TODO Auto-generated method stub
  s.setState(new StateB());
 }

 @Override
 public void nextStep(StateManager s) {
  // TODO Auto-generated method stub
  s.setState(new StateA());
 }

 @Override
 public String toString() {
  // TODO Auto-generated method stub
//  return super.toString();
  return "State C";
 }

}
4. 总结：

（1）采用interface实现多继承，加入管理类，方便状态切换

（2）应用场景：如果需要在 1、不同的状态(可能会对应相应的行为), 2、不同的行为;  间反复进行切换，则应优先考虑状态模式。