Java ThreadGroup isDaemon()用法及代码示例

ThreadGroup类isDaemon()方法

• isDaemon() 方法在 java.lang 包中可用。
• isDaemon() 方法用于检查该线程组是否为守护线程组。
• 正如我们所知，当它的最后一个线程被销毁或它的最后一个线程组被销毁时，守护线程组被隐式销毁。
• isDaemon() 方法是一个非静态方法，它只能通过类对象访问，如果我们尝试使用类名访问方法，那么我们将得到一个错误。
• isDaemon() 方法在检查此线程组的守护进程行为时不会抛出异常。

用法:

    public final boolean isDaemon();

参数：

• 它不接受任何参数。

返回值：

这个方法的返回类型是Boolean– 当该线程组是守护线程组时返回真，否则返回假。

例：

// Java program to demonstrate the example 
// of boolean isDaemon()method of ThreadGroup 

public class Daemon implements Runnable {
    public static void main(String[] args) {
        Daemon damn = new Daemon();
        damn.isDaemn();
    }

    public void isDaemn() {
        try {
            // Create two thread group and the named are base
            // and derived

            ThreadGroup base = new ThreadGroup("Base ThreadGroup");
            ThreadGroup derived = new ThreadGroup(base, "Derived ThreadGroup");

            // create two threads
            Thread th1 = new Thread(base, this);
            Thread th2 = new Thread(derived, this);

            // By using getName() method is to retrieve the
            // name of the thread th1
            System.out.println(th1.getName() + " " + "begins.....");

            // By using start() method is to start its execution 
            // of thread th1
            th1.start();

            // By using getName() method is to retrieve the
            // name of the thread th2
            System.out.println(th2.getName() + " " + "begins.....");

            // By using start() method is to start its execution 
            // of thread th2
            th2.start();

            System.out.println();

            // By using isDaemon() method is to check the
            // daemon status of the thread group
            boolean b1 = base.isDaemon();
            boolean b2 = derived.isDaemon();

            System.out.println("Is" + " " + base.getName() + " " + "daemon threadgroup:" + " " + b1);
            System.out.println("Is" + " " + derived.getName() + " " + "daemon threadgroup:" + " " + b2);


            // By using join() method is to wait the current
            // thread till complete execution of another
            // thread

            th1.join();
            th2.join();

        } catch (InterruptedException ex) {
            ex.printStackTrace();
        }

    }

    // Override run()
    public void run() {

        for (int k = 0; k < 100; ++k)
            ++k;

        System.out.println(Thread.currentThread().getName() + " " + "ends.....");
    }

}

输出

Thread-0 begins.....
Thread-0 ends.....
Thread-1 begins.....

Thread-1 ends.....
Is Base ThreadGroup daemon threadgroup:false
Is Derived ThreadGroup daemon threadgroup:false