java - UDP套接字处理

我在处理中编写UDP套接字的服务器端，每次在DatagramPacket receivePacket = new DatagramPacket(receiveData, 4096);行上都遇到NullPointerException。客户端是一个Python文件。这是服务器的代码。通过不同的处理文件调用方法setup()和draw()。

import processing.net.*;
import java.io.*;
import java.net.*;
import java.util.*;

//Server myServer;
DatagramSocket serverSocket;
byte[] receiveData;
InetAddress IPAddressList;
int portList = -1;

void setup(){
  try{
      DatagramSocket serverSocket = new DatagramSocket(21567);
  }
  catch (IOException e){
    e.printStackTrace();
    System.out.println(e);
  }

   byte[] receiveData = new byte[4096];
}

void draw(){

  float P1,P2,P3;
  print ("hello");
  try{
     DatagramPacket receivePacket = new DatagramPacket(receiveData, 4096);
     serverSocket.receive(receivePacket);
     String greeting = new String(receivePacket.getData());
     System.out.println("From Client: " + greeting);
     IPAddressList = receivePacket.getAddress();
     portList= receivePacket.getPort();
     P1 = Integer.valueOf(greeting);
     print(P1);
     print (greeting);
   }
   catch (IOException e){
    System.out.println(e.getMessage());
  }

  for (int i=0;i<receiveData.length;i++){
    print(receiveData[i]);
  }
}

最佳答案

您指出NullPointerException的行非常有帮助。

问题是您在外部范围中初始化了局部变量receiveData而不是字段receiveData。

解决方案是将byte[] receiveData = new byte[4096];行替换为receiveData = new byte[4096];。

通常，这称为名称重影:

http://en.wikipedia.org/wiki/Variable_shadowing

http://java.sun.com/docs/books/jls/third_edition/html/names.html#6.3.1

关于java - UDP套接字处理，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/7200032/