join 有三个重载方法 源码中的介绍：英文不太好，翻译的不知道可口不
public final void join(） throws InterruptedException // Waits for this thread to die. 表示等待该线程的终止
public final void join(long millis) throws InterruptedException // Waits at most {@code millis} milliseconds for this thread to * die. A timeout of {@code 0} means to wait forever. 等待该线程终止的时间最长为 millis 毫秒。超时如果为 0 线程要一直等下去。
public final void join(long millis,int nanos) throws InterruptedException * Waits at most {@code millis} milliseconds plus * {@code nanos} nanoseconds for this thread to die. 等待该线程终止的时间最长为 millis 毫秒 + nanos 纳秒。
yield
/** * A hint to the scheduler that the current thread is willing to yield * its current use of a processor. The scheduler is free to ignore this * hint. * * <p> Yield is a heuristic attempt to improve relative progression * between threads that would otherwise over-utilise a CPU. Its use * should be combined with detailed profiling and benchmarking to * ensure that it actually has the desired effect. * * <p> It is rarely appropriate to use this method. It may be useful * for debugging or testing purposes, where it may help to reproduce * bugs due to race conditions. It may also be useful when designing * concurrency control constructs such as the ones in the * {@link java.util.concurrent.locks} package. */为了防止一些线程独占CPU资源(这样其它的线程就得不到”响应”了). 可以让当前执行的线程”休息”一下.但是这种thread.yield() 调用, 并不保证下一个运行的线程就一定不是该线程. 可以考虑用Thread.sleep(long millis); 方法强制当前线程睡眠至少millis毫秒.
但是使用时要对该方法捕获. 调用方法很简单,只要在要睡眠的线程中加入 Thread.yield();
