Java中的异步和同步回调

Question

我正在尝试创建一个回调函数：

1. 首先，我创建了一个函数接口，用于定义回调函数的约定
2. 我创建了一个类，该类将定义一个方法来调用我的回调（我通过使用lambda表达式传递了接口的实现作为对此方法的引用）

下面是我的代码：

@FunctionalInterface
interface OnDumpEventListener {
    void onDumpEvent();
}

class SynchronousCallback {
    void doStuff(OnDumpEventListener callback) {
        System.out.println("i'm doing my work");

        if (callback != null) {
            callback.onDumpEvent();
        }
    }
}

class AsynchronousCallback {
    void doStuff(OnDumpEventListener callback) {
        System.out.println("i'm doing my work");
        try {
            wait(50);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        if (callback != null) {
            new Thread(() -> {
                callback.onDumpEvent();
            }).start();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        SynchronousCallback x = new SynchronousCallback();
        x.doStuff(() -> System.out.println("callback doing his work"));

        AsynchronousCallback y = new AsynchronousCallback();
        y.doStuff(() -> System.out.println("callback doing his work asynch"));
    }
}

但当我运行这段代码时，我得到了这样的结果。

i'm doing my work
callback doing his work
i'm doing my work
Exception in thread "main" java.lang.IllegalMonitorStateException
    at java.base/java.lang.Object.wait(Native Method)
    at callbacks.AsynchronousCallback.doStuff(Main.java:22)
    at callbacks.Main.main(Main.java:41)

有人能告诉我为什么我会有这个例外吗？

Answer 1

方法wait/notify/notifyAll必须在synchronized块内调用。