你知道java的main 方法启动后，会有多少个线程吗？

package com;

import java.util.stream.Stream;

/**
 * 你知道java的main 方法启动后，会有多少个线程吗？
 */
public class ThreadTest {
    public static void main(String[] args) throws InterruptedException {
        Thread mainThread = Thread.currentThread();
        ThreadGroup mainThreadThreadGroup = mainThread.getThreadGroup();
        //获取线程组中的线程。
        int count = mainThreadThreadGroup.activeCount();
        Thread[] threads = new Thread[count];
        mainThreadThreadGroup.enumerate(threads, true);
        System.out.println(count);
        Stream.of(threads).forEach(thread -> System.out.println(thread.getName()));
    }
}