手搓观察者模式-526互联

用专业的话来说，是这样的：观察者模式定义对象间的一种一对多依赖关系，使得每当一个对象状态发生改变时，其相关依赖对象皆得到通知并被自动更新。

用我自己的话说是这样的：法外狂徒张三欠了一屁股债，追债人不知道张三什么时候有钱还。但是张三是个很守信用的人，他一有了钱就会去通知追债人去还债。

即张三状态发生变化，相关的依赖对象（追债人）皆会被通知，并且更新~

上代码：

/**
 * @Author:Nyapii
 */
public class ObserverPattern {
    public static void main(String[] args) {
        Debit zhangSan = new ZhangSan();
        zhangSan.borrow(new Wangwu());
        zhangSan.borrow(new Lisi());
        zhangSan.notifyCredits();
    }
}
interface Debit{
    void borrow(Credit credit);
    void notifyCredits();
}

class ZhangSan implements Debit{

    private List<Credit> allCredits  = new ArrayList<>();
    private Integer state = 0; // 0表示没钱，1表示有钱

    @Override
    public void borrow(Credit credit) {
        allCredits.add(credit);
    }

    @Override
    public void notifyCredits() {
        allCredits.forEach(credit -> credit.takeMoney());
    }
}

interface Credit{
    void takeMoney();
}
class Lisi implements Credit{
    @Override
    public void takeMoney() {
        System.out.println("李四要钱！");
    }
}
class Wangwu implements Credit{
    @Override
    public void takeMoney() {
        System.out.println("王五要钱！");
    }
}

/**
 * @Author:Nyapii
 */
public class ObserverPattern {
    public static void main(String[] args) {
        Debit zhangSan = new ZhangSan();
        zhangSan.borrow(new Wangwu());
        zhangSan.borrow(new Lisi());
        zhangSan.notifyCredits();
    }
}
interface Debit{
    void borrow(Credit credit);
    void notifyCredits();
}

class ZhangSan implements Debit{

    private List<Credit> allCredits  = new ArrayList<>();
    private Integer state = 0; // 0表示没钱，1表示有钱

    @Override
    public void borrow(Credit credit) {
        allCredits.add(credit);
    }

    @Override
    public void notifyCredits() {
        allCredits.forEach(credit -> credit.takeMoney());
    }
}

interface Credit{
    void takeMoney();
}
class Lisi implements Credit{
    @Override
    public void takeMoney() {
        System.out.println("李四要钱！");
    }
}
class Wangwu implements Credit{
    @Override
    public void takeMoney() {
        System.out.println("王五要钱！");
    }
}

运行结果：