基本介绍
- 状态模式(State Pattern) :它主要用来解决对象在多种状态转换时，需要对外输出不同的行为的问题。状态和行为是一对应的，状态之间可以相互转换
-
当一个对象的内在状态改变时，允许改变其行为，这个对象看起来像是改变了其类
原理图：
image.png
1)Context 类为环境角色，用于维护State实例,这个实例定义当前状态
2)State 是抽象状态角色,定义一-个接口封装与Context的一一个特点接口相关行为
3)ConcreteState 具体的状态角色，每个子类实现一一个 与Context的一个状态相关行为
例子：
需求：
image.png
实现：
image.png
public abstract class State {
public abstract void deduceMoney();
public abstract boolean raffle();
public abstract void dispensePrize();
}
public class NoRaffleState extends State{
Active active;
public NoRaffleState(Active active) {
super();
this.active = active;
}
@Override
public void deduceMoney() {
// TODO Auto-generated method stub
System.out.println("积分扣除50，可以开始抽奖。。。");
active.setState(active.getCanRaffleState());
}
@Override
public boolean raffle() {
// TODO Auto-generated method stub
System.out.println("现在不可以抽奖，需要先扣除积分!!!");
return false;
}
@Override
public void dispensePrize() {
// TODO Auto-generated method stub
System.out.println("现在不可以领奖，请先抽奖!!!");
}
}
public class CanRaffleState extends State{
Active active;
public CanRaffleState(Active active) {
super();
this.active = active;
}
@Override
public void deduceMoney() {
// TODO Auto-generated method stub
System.out.println("积分已经扣除，请开始抽奖。。。");
}
@Override
public boolean raffle() {
// TODO Auto-generated method stub
Random random = new Random();
int num = random.nextInt(9);
if (num == 0) {
System.out.println("恭喜您抽中奖品！！！");
active.setState(active.getDispenseState());
return true;
}else{
System.out.println("很遗憾，您未抽中奖品。。。");
active.setState(active.getNoRaffleState());
return false;
}
}
@Override
public void dispensePrize() {
// TODO Auto-generated method stub
System.out.println("请先抽取奖品！！！");
}
}
public class DispenseState extends State{
Active active;
public DispenseState(Active active) {
// TODO Auto-generated constructor stub
this.active = active;
}
@Override
public void deduceMoney() {
// TODO Auto-generated method stub
System.out.println("您有奖品可以领取！！！");
}
@Override
public boolean raffle() {
// TODO Auto-generated method stub
System.out.println("您有奖品可以领取！！！");
return false;
}
@Override
public void dispensePrize() {
// TODO Auto-generated method stub
int num = active.getCount();
if (num > 0 ) {
System.out.println("您的奖品已经领取！！！");
active.setState(active.getNoRaffleState());
if (num == 1) {
System.out.println("奖品已经发放完了，活动结束！！！");
active.setState(active.getDispenseOutState());
}
}
}
}
public class DispenseOutState extends State{
Active active;
public DispenseOutState(Active active) {
super();
this.active = active;
}
@Override
public void deduceMoney() {
// TODO Auto-generated method stub
System.out.println("奖品已经发放完。。。");
}
@Override
public boolean raffle() {
// TODO Auto-generated method stub
System.out.println("奖品已经发放完。。。");
return false;
}
@Override
public void dispensePrize() {
// TODO Auto-generated method stub
System.out.println("奖品已经发放完。。。");
}
}
public class Active {
State state;
NoRaffleState noRaffleState = new NoRaffleState(this);
CanRaffleState canRaffleState = new CanRaffleState(this);
DispenseState dispenseState = new DispenseState(this);
DispenseOutState dispenseOutState = new DispenseOutState(this);
int count = 0;
public Active(int count) {
super();
state = getNoRaffleState();
this.count = count;
}
public boolean raffle() {
// TODO Auto-generated method stub
state.deduceMoney();
if (state.raffle()) {
state.dispensePrize();
return true;
}
return false;
}
public int getCount(){
int temp = count;
count--;
return temp;
}
public void setState(State state) {
this.state = state;
}
public State getState() {
return state;
}
public NoRaffleState getNoRaffleState() {
return noRaffleState;
}
public CanRaffleState getCanRaffleState() {
return canRaffleState;
}
public DispenseState getDispenseState() {
return dispenseState;
}
public DispenseOutState getDispenseOutState() {
return dispenseOutState;
}
}
public class Client {
public static void main(String[] args) throws InterruptedException {
Active active = new Active(2);
for(int i=0; i<30;i++){
System.out.println("第"+(i+1)+"次抽奖："+active.raffle());
}
}
}
状态模式的注意事项和细节
- 代码有很强的可读性。状态模式将每个状态的行为封装到对应的一个类中
- 方便维护。将容易产生问题的if-else语句删除了，如果把每个状态的行为都放到- -个类中，每次调用方法时都要判断当前是什么状态，不但会产出很多if-else语句，.而且容易出错
- 符合“开闭原则”。容易增删状态
- 会产生很多类。每个状态都要一个对应的类，当状态过多时会产生很多类，加大维护难度
- 当一个事件或者对象有很多种状态，状态之间会相互转换，对不同的状态要求有不同的行为的时候，可以考虑使用状态模式
