在main函數(shù)里面調(diào)用了join，查看了join的源碼，調(diào)用join會(huì)轉(zhuǎn)換為調(diào)用wait(0)，比如下面的代碼 public static void main(String[] args) { Thread r1 = new Thread(new X("r1")) r1.start(); try { r1.join(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Main finished"); } 但是，一般說(shuō)A調(diào)用了wait則需要使用notify或者notifyAll喚醒線程A，而在join的代碼當(dāng)中并沒(méi)有看到這兩個(gè)函數(shù)對(duì)main線程的notify，那么main是怎么從join里面的wait(0)出來(lái)再進(jìn)行循環(huán)判斷的？（下面是join的源碼，調(diào)用join()，在join()內(nèi)部會(huì)直接調(diào)用join(0)，也就是下面這個(gè)函數(shù)） public final synchronized void join(long millis) throws InterruptedException { long base = System.currentTimeMillis(); long now = 0; if (millis < 0) { throw new IllegalArgumentException("timeout value is negative"); } if (millis == 0) { while (isAlive()) { wait(0); } } else { while (isAlive()) { long delay = millis - now; if (delay <= 0) { break; } wait(delay); now = System.currentTimeMillis() - base; } } }