多线程同步中wait()方法抛出IllegalMonitorStateException异常的原因是什么？

package 并发编程.work2;

public class Test {
    private static volatile String CURRENT_THREAD = "A";

    public static void main(String[] args) {
        Thread t1 = new Thread(new PrintThreadName(), "A");
        Thread t2 = new Thread(new PrintThreadName(), "B");
        Thread t3 = new Thread(new PrintThreadName(), "C");
        t1.start();
        t2.start();
        t3.start();
    }

    static class PrintThreadName implements Runnable {
        @Override
        public void run() {
            for (int i = 0; i < 5; i++) {
                synchronized (CURRENT_THREAD) {
                    if (!Thread.currentThread().getName().equals(CURRENT_THREAD)) {
                        try {
                            CURRENT_THREAD.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    System.out.println(Thread.currentThread().getName());
                    CURRENT_THREAD = getNextThread(CURRENT_THREAD);
                    CURRENT_THREAD.notifyAll();
                }
            }
        }

        private String getNextThread(String current) {
            switch (current) {
                case "A":
                    return "B";
                case "B":
                    return "C";
                case "C":
                    return "A";
                default:
                    return "A";
            }
        }
    }
}

private static final Object lock = new Object(); // 使用独立的锁对象

synchronized (lock) {
    // ... your code here ...
}