public static class ThreadPrinter implements Runnable {
private String name;
private Object prev;
private Object self;
private ThreadPrinter(String name, Object prev, Object self) {
this.name = name;
this.prev = prev;
this.self = self;
}
@Override
public void run() {
int count = 3;
//打印次数
while (count > 0) {//多线程并发，不能用if，必须用循环测试等待条件，避免虚假唤醒
synchronized (prev) { // 先获取 prev 锁
synchronized (self) {// 再获取 self 锁
System.out.print(name);
count--;
self.notifyAll();// 先释放 self，唤醒其他线程竞争self锁
}
try {
prev.wait(); // 再释放 prev，休眠等待唤醒
/**
* 注意的是notify()调用后，并不是马上就释放对象锁，而是在相应的synchronized(){}语句块执行结束，自动释放锁，
* JVM会在wait()对象锁的线程中随机选取一线程，赋予其对象锁，唤醒线程，继续执行。
*/
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
public static void main(String[] args) throws Exception {
Object a = new Object();
Object b = new Object();
Object c = new Object();
ThreadPrinter pa = new ThreadPrinter("A", c, a);
ThreadPrinter pb = new ThreadPrinter("B", a, b);
ThreadPrinter pc = new ThreadPrinter("C", b, c);
new Thread(pa).start();
// Thread.sleep(3);
new Thread(pb).start();
// Thread.sleep(10);
new Thread(pc).start();
// Thread.sleep(10);
}
