程序如下：

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public?static?void?main(String[]?args)?throws??Exception{ ????final?List?list?=?new?ArrayList(); ????final?Object?lock?=?new?Object(); ????Thread?t1?=?new?Thread(new?Runnable()?{ ????????@Override ????????public?void?run()?{ ????????????synchronized?(lock){ ????????????????for(int?i?=?0?;?i?<?10?;?i++){ ????????????????????list.add(i); ????????????????????if(list.size()?==?5){ ????????????????????????lock.notify(); ????????????????????????System.out.println(Thread.currentThread().getName()?+?"發(fā)出通知!"); ????????????????????} ????????????????} ????????????} ????????????System.out.println(Thread.currentThread().getName()?+?"execute?over!"); ????????} ????}); ????Thread?t2?=?new?Thread(new?Runnable()?{ ????????@Override ????????public?void?run()?{ ????????????synchronized?(lock){ ????????????????if(list.size()?!=?5){ ????????????????????try?{ ????????????????????????lock.wait(); ????????????????????}?catch?(InterruptedException?e)?{ ????????????????????????e.printStackTrace(); ????????????????????} ????????????????} ????????????????System.out.println(Thread.currentThread().getName()?+?"?收到通知!"); ????????????} ????????????System.out.println(Thread.currentThread().getName()?+?"execute?over!"); ????????} ????}); ????t2.start(); ????Thread.sleep(1000); ????t1.start(); }

分析：

程序的意圖本是利用多線程之間的通信，利用wait/notify實現(xiàn)，可是運行的結(jié)果是雖然線程T1發(fā)出了通知，但是線程T2并沒有立即收到通知進行執(zhí)行，這是為什么呢？?因為只有線程T1執(zhí)行完畢釋放了鎖，T2才能執(zhí)行，那么也就是說wait/notify并不是實時的（wait釋放了鎖，而notify沒有釋放鎖導致的），那么線程之間實時的通信該怎么做呢？可以利用CountDownLatch來實現(xiàn)。

對程序的改進：

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public?static?void?main(String[]?args)?throws??Exception{ ????final?List?list?=?new?ArrayList(); ????final?Object?lock?=?new?Object(); ????final?CountDownLatch?countDownLatch?=?new?CountDownLatch(1); ????Thread?t1?=?new?Thread(new?Runnable()?{ ????????@Override ????????public?void?run()?{ ????????????????for(int?i?=?0?;?i?<?10?;?i++){ ????????????????????list.add(i); ????????????????????if(list.size()?==?5){ ????????????????????????countDownLatch.countDown(); ????????????????????????System.out.println(Thread.currentThread().getName()?+?"發(fā)出通知!"); ????????????????????} ????????????????} ????????????System.out.println(Thread.currentThread().getName()?+?"execute?over!"); ????????} ????}); ????Thread?t2?=?new?Thread(new?Runnable()?{ ????????@Override ????????public?void?run()?{ ????????????????if(list.size()?!=?5){ ????????????????????try?{ ????????????????????????countDownLatch.await(); ????????????????????}?catch?(InterruptedException?e)?{ ????????????????????????e.printStackTrace(); ????????????????????} ????????????????System.out.println(Thread.currentThread().getName()?+?"?收到通知!"); ????????????} ????????????System.out.println(Thread.currentThread().getName()?+?"execute?over!"); ????????} ????}); ????t2.start(); ????Thread.sleep(1000); ????t1.start(); }

本文轉(zhuǎn)自zfz_linux_boy 51CTO博客，原文鏈接：http://blog.51cto.com/zhangfengzhe/1875221，如需轉(zhuǎn)載請自行聯(lián)系原作者

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