为什么线程组 为空。求解

Question

public class TestRunnable implements Runnable{

@Override
public void run() {
   System.out.println("我实现了Runnable接口");        
}

public static void main(String[] args) throws InterruptedException{
    TestRunnable tr=new TestRunnable();
    ThreadGroup tg=new ThreadGroup("线程组1");
    Thread tt=new Thread(tg,tr,"线程1");
    tt.start();
    tt.sleep(2000);
    //优先级
    int priority=tt.getPriority();
    //名称
    String name=tt.getName();
    //id
    long id=tt.getId();
    System.out.println("此线程的优先级是"+priority+"  此线程的名称"+name+"  此线程的id"+id);

    //栈追踪元
    StackTraceElement[] arr=tt.getStackTrace();
    for(StackTraceElement ele:arr){
        String eleClassName=ele.getClassName();
        String FileName=ele.getFileName();
        int lineNumber=ele.getLineNumber();
        String eleMethodName=ele.getMethodName();
        System.out.println("栈追踪元eleClassName="+eleClassName+"   FileName"+FileName
                +"  lineNumber="+lineNumber+"   eleMethodName"+eleMethodName);              
    }
    //所属线程组
    ThreadGroup group= tt.getThreadGroup();
    if(group!=null){
        int maxPriority=group.getMaxPriority();
        String groupName=group.getName();
        System.out.println("最大优先级"+maxPriority+" groupName"+groupName);
    }
}

}

Answer 1

因为你的线程在sleep之后就结束了。