[英]nullpointer exception for thread
I am implementing a tcp java client/server app based on a tut on the internet I changed some methods and get error of nullpointerexception 我正在基于互联网上的tut实现一个tcp java客户端/服务器应用程序我改变了一些方法并得到nullpointerexception的错误
The error comes from the run(). 错误来自run()。 Its in a Connection class that extends the Thread class.
它在一个扩展Thread类的Connection类中。 run() is supposed to listen to incoming communication.
run()应该监听传入的通信。 I start the server class, listen to a port.
我启动服务器类,听一个端口。 So I have a succefful connection.
所以我有一个成功的联系。 Then the app reports error when I try to listen to incoming communication through the run() method
然后,当我尝试通过run()方法侦听传入通信时,应用程序报告错误
establish a connection and start: 建立连接并开始:
Connection c = new Connection(host,port);
Scanner chatConsole = new Scanner(System.in);
String text = "";
while (!text.equalsIgnoreCase("halt")){
text = chatConsole.nextLine();
c.start();
Exception in thread "Thread-1" java.lang.NullPointerException 线程“Thread-1”中的异常java.lang.NullPointerException
The run() 运行()
public void run(){//watch for incoming communication
String msg;
try{//loop reading lines and display msg
while ((msg = in.readLine()) != null) {
System.out.println(msg);
}
}catch (IOException e) {
System.err.println(e);
}
}
This is the constructor for the class if its helpful to debug. 如果它有助于调试,那么这是该类的构造函数。
public Connection(String iniName, int iniPort){
host = iniName;
port = iniPort;
try {
server = new Socket(host, port);
}catch (UnknownHostException e){
System.err.println(e);
System.exit(1);
}
try{
stdIn = new BufferedReader(new InputStreamReader(System.in));
PrintWriter out = new PrintWriter(server.getOutputStream(), true); //output stream to server
BufferedReader in = new BufferedReader(new InputStreamReader(server.getInputStream()));
}catch(Exception e){
System.err.println(e);
}
}
Thank you 谢谢
Your in
variable is null, where you try to use it: 您的
in
变量为null,您尝试使用它:
while ((msg = in.readLine()) != null) {
possibly because you're shadowing it where you construct it. 可能是因为你正在构建它的地方遮蔽它。
BufferedReader in = new BufferedReader(new InputStreamReader(server.getInputStream()));
Instead don't re-declare the variable locally: 而不是在本地重新声明变量:
in = new BufferedReader(new InputStreamReader(server.getInputStream()));
Nowhere in the code you've pasted do you declare a global field in
. 无处在你的代码粘贴好你声明一个全局场
in
。 Is that the line that's throwing the NullPointerException
? 这是抛出
NullPointerException
吗? ( in.readLine
). (
in.readLine
)。 Please make sure that Stream is initialized correctly (ie make it a field, not a local variable in the constructor) 请确保正确初始化Stream(即将其设为字段,而不是构造函数中的局部变量)
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