程序中创建了主程序线程、thread1和thread2三个线程，thread1是ThreadUseExtends类的对象，通过继承Thread实现线程，thread2是ThreadUseRunnable类的对象，通过实现Runnable接口实现线程，主程序主线程睡眠7秒，thread1线程睡眠10秒，thread2睡眠1秒，程序执行过程中首先执行主线程，由主线程启动thread1，thread1启动后，需要睡眠10秒，接着主线程睡眠7秒，那么势必主线程醒来时thread1还处于睡眠状态，所以thread1被杀掉了。接着主线程启动thread2，thread2启动后，需要睡眠1秒，接着主线程睡眠7秒，那么当主线程醒来时thread2已经醒来并执行完成，所以主线程没有发现thread2。-Program to create the main program threads, thread1 and thread2 three Thread, thread1 is ThreadUseExtends objects of a class, through inheritance Thread realize Thread, thread2 is ThreadUseRunnable objects of a class, by implementing Runnable interface implementation Thread, the main program main Thread to sleep 7 seconds and thread1 Thread to sleep 10 seconds, thread2 sleep 1 second, during the execution of the first executive main Thread, the main Thread start thread1, thread1 start, need sleep 10 seconds, then the main Thread to sleep 7 seconds, then the main Thread will wake up thread1 is still in a state of sleep, so thread1 was killed. Then the main thread start thread2, thread2 start, need sleep 1 second, then the main thread to sleep 7 seconds and then when main thread woke up thread2 have to wake up and the implementation of the completion, so the main thread found no thread2.