简单的"Hello Word"用了几个线程

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello Word!");
         //获取threadMXBean
        ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();
        long[] allThreadIds = threadMXBean.getAllThreadIds();
         //根据ThreadId获取线程信息
        ThreadInfo[] threadInfos = threadMXBean.getThreadInfo(allThreadIds);
        for (ThreadInfo threadInfo:threadInfos) {
            //打印线程id和线程名称 
            System.out.println(threadInfo.getThreadId()+":"+threadInfo.getThreadName());
        }
    }
}

Hello Word!
5:Monitor Ctrl-Break
4:Signal Dispatcher
3:Finalizer
2:Reference Handler
1:main

$javac HelloDemo.java 
$ java HelloDemo
Hello Word!
4:Signal Dispatcher
3:Finalizer
2:Reference Handler
1:main