java - 是什么导致线程 "pool-1-thread-2"中出现异常(NullPointerException)

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 6 年前。

我正在创建一个多线程网络服务器。当我运行客户端时，我收到 NullPointException。为什么会发生这种情况以及可以采取什么措施来解决它？

Concerning the suggestions that I should read the mentioned tutorial. I have tried to solve the problem with the help of it. I created a constructor, but then I didn't know how to call the class:
theExecutor.execute(new Broadcaster (connection);

I also created a setter: public void setQuestions(String[]
questions) {
this.questions[1] = questions[1];}

That didn't help either. The String is initialized at the same place as questions[0]. I can print out questions[1] in the console. It get's its value from the ArrayList, but I do not know how to pass that value to the HandleValidation class. That seems to be the problem. If I have missed something in the tutorial that is an obvious solution, please tell me!

在这里您可以阅读异常消息和堆栈跟踪:

Exception in thread "pool-1-thread-2" java.lang.NullPointerException
at HandlleValidation.run(QuizServer.java:121)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745

这里我正在初始化处理线程的执行器:

public class QuizServer {
public static void main(String[] args) throws IOException {

ExecutorService theExecutor = Executors.newFixedThreadPool(10000);
    ServerSocket quizSocket = new ServerSocket(serverPort);

    try {
        while (true) {  //Skriver ut While True
            Socket connection = quizSocket.accept();
            theExecutor.execute(new Broadcaster(connection));
            theExecutor.execute(new HandlleValidation(connection));
        }

字符串问题[1]的起源位于 Broadcaster 类中:

我正在使用 get 和 set 方法来使其他内部类能够使用

String questions[];

static class Broadcaster extends Thread {

    String quizFile = "src/qa.txt";
    private Socket connection;

    private PrintStream write;
    private String answer;
    private String questions[];
    int points = 0;

    public String[] getQuestions() {
        return questions;
    }

Here are the Strings questions[0] and questions[1]created:

while (true) {

                    for (String string : questionsList) {
                        String[] questions = string.split("/");
                        write.println(questions[0]);  //Printing out in client.
                        try {
                            Thread.sleep(4000); //"Sleeping" between the lines.
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }

NullPointerException 发生在 HandleValidation 类中:

class HandlleValidation extends Thread {

问题是由这一行引起的:

  if (answer.equals(questions[1])) {
                points++;
                writer.println("RÄTT SVAR! Du har " + points + " poäng");

二传手:

public void setQuestions(String[] questions) {
    this.questions = questions;

I have tried to include as little of the code as possible to describe the problem. I may be able to give more information if requested!

Answer 1

我在 for (String string: questionsList) { 的上下文中看到该变量，并且在另一个时刻您在 if (answer.equals (questions [1])) {:即在其他上下文中，在其他范围内。

我的建议是将该变量声明在 for 范围之外。