ThreadGroup.activeCount()方法在java中不起作用

Question

我正在学习多线程的概念，我试图在数组中找到活动线程的数量，但ThreadGroup.activeCount((的方法只返回零值。

这是代码：

线程对象类：-

class th1 extends Thread
{
public th1(String threadName, ThreadGroup tg1)
{
super(tg1, threadName);
}
@Override
public void run() 
{
try {
Thread.sleep(5000);
} 
catch (InterruptedException e) 
{
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + " is running");
}
}

主类：-

public class enumerate_demo 
{
public static void main(String[] args) 
{
ThreadGroup tg1 = new ThreadGroup("group 1");
Thread t1 = new Thread(new th1("t-1", tg1));
t1.start();
Thread t2 = new Thread(new th1("t-2", tg1));
t2.start();
Thread t3 = new Thread(new th1("t-3", tg1));
t3.start();
System.out.println("Number of active count :- " + tg1.activeCount());
Thread[] group = new Thread[tg1.activeCount()];
int count = tg1.enumerate(group);
for (int i = 0; i < count; i++)
{
System.out.println("Thread " + group[i].getName());
}
}
}

Answer 1

问题是，在创建实例th1类时，您将它们用作Runnable，而不是Thread。并且这些包装器线程与任何ThreadGroup都没有关联。按如下方式声明变量。

Thread t1 = new th1("t-1", tg1);
t1.start();