是什么导致线程"pool-1-thread-2"中的异常? (空指针异常) [英] What is causing the Exception in thread "pool-1-thread-2" (NullPointerException)
问题描述
我正在创建一个多线程的Web服务器.当我运行客户端时,我收到一个NullPointException.为什么会发生这种情况,该怎么办才能解决呢?
关于我应该阅读上述教程的建议.我有 试图借助它来解决问题.我创建了一个 构造函数,但后来我不知道如何调用该类:
theExecutor.execute(new Broadcaster (connection);
我还创建了一个setter:
public void setQuestions(String[] questions) { this.questions[1] = questions[1];}
那也没有帮助.字符串在同一位置初始化 作为
questions[0]
.我可以在控制台中打印questions[1]
.它 从ArrayList获取它的值,但是我不知道如何传递它 HandleValidation类的值.这似乎是问题所在. 如果我错过了本教程中明显的解决方案,请告诉我!
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
在这里,我正在初始化正在处理线程的Executor:
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]的起源在Broadcaster类中:
我正在使用get和set方法,以使另一个内部类可以使用
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;
}
以下是创建的字符串
questions[0]
和questions[1]
:
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 {
问题是由以下行引起的:
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;
我试图尽量减少描述的代码 问题.如果需要,我也许可以提供更多信息!
我在for (String string: questionsList) {
的上下文中看到了该变量,并且又在您在if (answer.equals (questions [1])) {
中使用它了:即在其他上下文中,在其他范围内. /p>
我的建议是将该变量声明为 for
范围之外.
I am creating a multi-threaded web server. When I run the client I receive a NullPointException. Why is this happening and what can be done to solve it?
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 outquestions[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!
Here you can read exception message and the stack trace:
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
Here I am initializing the Executor which are handling the threads:
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));
}
The origin of the String questions[1] is in the Broadcaster class:
I am using a get and set method to make it possible for the other inner class to work with
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]
andquestions[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();
}
The NullPointerException occurs in the HandleValidation class:
class HandlleValidation extends Thread {
The problem is caused by this line:
if (answer.equals(questions[1])) {
points++;
writer.println("RÄTT SVAR! Du har " + points + " poäng");
The Setter:
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!
I see the variable in context of for (String string: questionsList) {
and in another moment you use it in if (answer.equals (questions [1])) {
: that is in other context, in other scope.
My suggestion is to declare that variable out of the for
scope.
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