Java ThreadGroup getParent()用法及代码示例

ThreadGroup类getParent()方法

• getParent() 方法在 java.lang 包中可用。
• getParent() 方法用于返回此线程组的父级。
• getParent() 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。
• getParent() 方法可能会在返回此 ThreadGroup 的父级时抛出异常。
  SecurityException– 当不允许当前线程更新此线程组时，可能会抛出此异常。

用法:

    public final ThreadGroup getParent();

参数：

• 它不接受任何参数。

返回值：

这个方法的返回类型是ThreadGroup– 它返回这个 "ThreadGroup" 的父级，或者当没有这个线程组的父级时它返回 null。

例：

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

public class GetParent implements Runnable {
    public static void main(String[] args) {
        GetParent gp = new GetParent();
        gp.parent();
    }

    public void parent() {
        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 getParent() method is to return the
            // parent of the base and derived thread group

            System.out.println("base.getParent():" + " " + base.getParent().getName());
            System.out.println("derived.getParent():" + " " + derived.getParent().getName());


            // 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.....
base.getParent():main
derived.getParent():Base ThreadGroup