设计模式——状态模式

什么是状态模式

一个事物在发展过程中都会产生不同的状态，比如人在成长过程中会有小孩，成人，老人等状态。但是这个状态是依赖聚合于对象本身的，因为状态是随着对象的行为而发生变化的，状态本身就是对象的一部分。

UML图

代码示例

public class RaffleActivity {

  private State state;

  private int count;


  private State canRaffleState = new CanRaffleState(this);

  private State noRaffleState = new NoRaffleState(this);

  private State dispenseState = new DispenseState(this);

  private State dispenseOutState = new DispenseOutState(this);

  public RaffleActivity(int count) {
    this.state = this.noRaffleState;
    this.count = count;
  }

  public void deduceMoney() {
    state.deduceMoney();
  }

  public void raffle() {
    if (state.raffle()) {
      state.dispensePrize();
    }
  }

  public State getState() {
    return state;
  }

  public void setState(State state) {
    this.state = state;
  }

  public int getCount() {
    return count;
  }

  public void setCount(int count) {
    this.count = count;
  }

  public State getCanRaffleState() {
    return canRaffleState;
  }

  public void setCanRaffleState(State canRaffleState) {
    this.canRaffleState = canRaffleState;
  }

  public State getNoRaffleState() {
    return noRaffleState;
  }

  public void setNoRaffleState(State noRaffleState) {
    this.noRaffleState = noRaffleState;
  }

  public State getDispenseState() {
    return dispenseState;
  }

  public void setDispenseState(State dispenseState) {
    this.dispenseState = dispenseState;
  }

  public State getDispenseOutState() {
    return dispenseOutState;
  }

  public void setDispenseOutState(State dispenseOutState) {
    this.dispenseOutState = dispenseOutState;
  }
}

public interface State {

  void deduceMoney();

  boolean raffle();

  void dispensePrize();

}


public class NoRaffleState implements State{

  private RaffleActivity raffleActivity;

  public NoRaffleState(RaffleActivity raffleActivity) {
    this.raffleActivity = raffleActivity;
  }

  @Override
  public void deduceMoney() {
    System.out.println("扣除50元余额，您可以开始抽奖了。");
    raffleActivity.setState(raffleActivity.getCanRaffleState());
  }

  @Override
  public boolean raffle() {
    System.out.println("当前不可以抽奖。");
    return false;
  }

  @Override
  public void dispensePrize() {
    System.out.println("不能发放奖品。");
  }
}

public class CanRaffleState implements State {

  private RaffleActivity raffleActivity;

  public CanRaffleState(RaffleActivity raffleActivity) {
    this.raffleActivity = raffleActivity;
  }

  @Override
  public void deduceMoney() {
    System.out.println("您已抽中奖品。");
  }

  @Override
  public boolean raffle() {
    if (raffleActivity.getCount() < 0) {
      System.out.println("抽奖活动已结束！请下次再来！");
      System.exit(0);
    }
    Random random = new Random();
    int num = random.nextInt(10);
    if (num == 0) {
      System.out.println("恭喜您！中奖了！");
      raffleActivity.setCount(raffleActivity.getCount() - 1);
      raffleActivity.setState(raffleActivity.getDispenseState());
      return true;
    } else {
      System.out.println("很遗憾！未中奖！");
      raffleActivity.setState(raffleActivity.getNoRaffleState());
      return false;
    }
  }

  @Override
  public void dispensePrize() {
    System.out.println("请先抽奖！");
  }
}

public class DispenseState implements State {

  private RaffleActivity raffleActivity;

  public DispenseState(RaffleActivity raffleActivity) {
    this.raffleActivity = raffleActivity;
  }

  @Override
  public void deduceMoney() {
    System.out.println("您已抽中奖品！");
  }

  @Override
  public boolean raffle() {
    System.out.println("您已抽中奖品！");
    return false;
  }

  @Override
  public void dispensePrize() {
    System.out.println("正在发送奖品！请稍等！");
    raffleActivity.setState(raffleActivity.getDispenseOutState());
  }
}

public class DispenseOutState implements State {

  private RaffleActivity raffleActivity;

  public DispenseOutState(RaffleActivity raffleActivity) {
    this.raffleActivity = raffleActivity;
  }

  @Override
  public void deduceMoney() {
    System.out.println("您已抽中奖品");
  }

  @Override
  public boolean raffle() {
    System.out.println("您已抽中奖品");
    return false;
  }

  @Override
  public void dispensePrize() {
    System.out.println("奖品已发送完毕！");
  }
}

public class Client {


  public static void main(String[] args) {
    RaffleActivity raffleActivity = new RaffleActivity(3);

    for (int i = 0; i < 15; i++) {
      System.out.println("这是第" + i + "次抽奖");

      raffleActivity.deduceMoney();
      raffleActivity.raffle();
    }


  }

}