java - 线程.getState()

Question

我是使用线程的新手，我正在尝试找出一种方法来判断线程是否终止，以及从线程收集一些信息。但是，每当我尝试调用其中一个线程的方法(包括 thread.getState())时，我都会收到空指针异常。请我想了解一下线程在 java 中如何工作以及我如何使用它的一些见解。

public class MatrixThread extends Thread{

private int num;
private String ref;
private boolean finished;
JsonObject json = new JsonObject();

public MatrixThread(int number){
    super("Matrix Thread");
    System.out.println("Running Thread: " +number);
    num = number;
    json = object;
    finished = false;
    start();
}

public void run(){
    System.out.println("Thread #" + num + "Has begun running");
    boolean again = true;

    while(again){
            //Does something
            if(wasSuccessful()) {
                ref = operation
                System.out.println("Success");
                finished = true;
            } else System.out.println("Did not work try again");
        } catch (IOException e) {
            System.out.println("Error, Try again");
        }
    }
}

public boolean isFinished(){
    return finished;
}

public String getRef(){
    return ref;
}

public int getNum(){
    return num;
}
}

然后当我运行我的程序时，它看起来像这样

public static void main(String[] args) {
    MatrixThread[] threads = new MatrixThread[10];

    String[] refs = new String[100];
    int count = 0;
    for(MatrixThread thread : threads){
        thread = new MatrixThread(count);
        count++;
    }

    while(count < 100){
        for(MatrixThread thread : threads){
            if(thread.getState() == Thread.State.TERMINATED){
                refs[thread.getNum()] = thread.getRef();
                thread = new MatrixThread(count);
                count++;
            }
        }
    }

}

由于空指针异常，主进程中的执行在“thread.getState()”处停止。有什么想法吗？

Answer 1

您没有将线程数组中的索引分配给非空值。您创建它们，但从未将它们分配给数组中的索引，因此这些索引为空。

这是对您的代码的更正:

for(int i=0;i<threads.length;i++){
    MatrixThread thread = new MatrixThread(count);
    threads[i] = thread;
    count++;
}

我不建议扩展线程。尝试实现 runnable，并将 runnable 传递给线程。我可以详细说明原因 but its already been done.

Thread.isAlive 可能就是您正在寻找的。我建议做类似的事情......

runnable.setActive(false);
//this will block invoking thread for 1 second, or until the threadRunningRunnable terminates
threadRunningRunnable.join(1000);
//for the paranoid programmer...
if(threadRunningRunnable.isAlive()){
    //something very bad happened.
}