使用多线程和不使用多线程的区别程序：Counter.java没有使用多线程，Close按钮不起作用，CounterThread.java，使用了多线程，可以使用Close按钮关闭程序-Use multi-threaded and multithreaded diff program: Counter.java did not use multi-threading, the Close button does not work, CounterThread.java, using multi-t