Question

package com.threads;

import java.util.Arrays;
import java.util.Map;

public class TestThread extends Thread {
    public void run() {
        Map<Thread, StackTraceElement[]> map = Thread.getAllStackTraces();
        for(Thread s: map.keySet()){
            System.out.println(s + Arrays.toString(map.get(s)));
        }

    }

    public static void main(String[] args) {
        TestThread testThread = new TestThread();
        Map<Thread, StackTraceElement[]> map = Thread.getAllStackTraces();
        for(Thread s: map.keySet()){
            System.out.println(s + Arrays.toString(map.get(s)));
        }
        System.out.println("-----------------------------------------");
        testThread.start();     
    }

}

Thread[main,5,main][java.lang.Thread.dumpThreads(Native Method), java.lang.Thread.getAllStackTraces(Unknown Source), com.threads.TestThread.main(TestThread.java:17)]
Thread[Finalizer,8,system][java.lang.Object.wait(Native Method), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)]
Thread[Reference Handler,10,system][java.lang.Object.wait(Native Method), java.lang.Object.wait(Unknown Source), java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)]
Thread[Attach Listener,5,system][]
Thread[Signal Dispatcher,9,system][]

---------------------------------
Thread[Thread-0,5,main][java.lang.Thread.dumpThreads(Native Method), java.lang.Thread.getAllStackTraces(Unknown Source), com.threads.TestThread.run(TestThread.java:8)]
Thread[Finalizer,8,system][java.lang.Object.wait(Native Method), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)]
Thread[Reference Handler,10,system][java.lang.Object.wait(Native Method), java.lang.Object.wait(Unknown Source), java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)]
Thread[Attach Listener,5,system][]
Thread[Signal Dispatcher,9,system][]

自从我开始一个新线程以来，我希望在我正在打印的Map中找到另一个条目。但是线程的数量保持不变。

Answer 1

数字保持不变，但是出现了一个新线程：Thread-0，另一个已经消失：main。

这是预料之中的，因为一旦主方法返回主线程就会退出，而Thread-0就是你已经开始的线程。

Answer 2

线程数相同，因为您的主线程已在TestThread正在访问Thread.getAllStackTraces()的位置完成了该作业。

在主要帖子中，您可以join()并等待TestThread完成。

public static void main(String[] args) throws InterruptedException {
    TestThread testThread = new TestThread();
    Map<Thread, StackTraceElement[]> map = Thread.getAllStackTraces();
    for(Thread s: map.keySet()){
        System.out.println(s + Arrays.toString(map.get(s)));
    }
    System.out.println("-----------------------------------------");
    testThread.start();     
    testThread.join();
}

产生以下结果：

Thread[main,5,main][java.lang.Thread.dumpThreads(Native Method), java.lang.Thread.getAllStackTraces(Unknown Source), code.TestThread.main(TestThread.java:17)]
Thread[Attach Listener,5,system][]
Thread[Signal Dispatcher,9,system][]
Thread[Reference Handler,10,system][java.lang.Object.wait(Native Method), java.lang.Object.wait(Object.java:503), java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)]
Thread[Finalizer,8,system][java.lang.Object.wait(Native Method), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)]
-----------------------------------------
Thread[main,5,main][java.lang.Object.wait(Native Method), java.lang.Thread.join(Unknown Source), java.lang.Thread.join(Unknown Source), code.TestThread.main(TestThread.java:23)]
Thread[Attach Listener,5,system][]
Thread[Signal Dispatcher,9,system][]
Thread[Thread-0,5,main][java.lang.Thread.dumpThreads(Native Method), java.lang.Thread.getAllStackTraces(Unknown Source), code.TestThread.run(TestThread.java:8)]
Thread[Reference Handler,10,system][java.lang.Object.wait(Native Method), java.lang.Object.wait(Object.java:503), java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)]
Thread[Finalizer,8,system][java.lang.Object.wait(Native Method), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.ReferenceQueue.remove(Unknown Source), java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)]

有人可以解释这个程序的控制台输出吗？

2 个答案: