我的问题如下：我有以下客户端类：
import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;
public class Client {
public final int portNumber = 6040;
public Socket socket;
private PrintWriter pw;
/**
* @param args
* @throws IOException
*/
public void connect() throws IOException{
// du kan vælge at bruge inetadressen til at connecte i socketet.
InetAddress adr = InetAddress.getByName("localhost");
socket = new Socket("localhost", portNumber);
pw = new PrintWriter(socket.getOutputStream());
pw.println("Connected waiting for input");
pw.flush();
}
/**
* This method sends the message (that the client(chat person) writes to the user)
* @param x
* @throws NullPointerException
* @throws IOException
*/
public void SendChat(String x) throws NullPointerException{
pw.print(x);
pw.flush();
}
public int sendCommando(int id) throws IOException{
PrintWriter pw = new PrintWriter(socket.getOutputStream());
pw.print(id);
/*
* this part of the program sends a command to the server if the command is 1 then 1 is = Connect.
* the program then ask the server is the server is full or is it ok to connect?
* if the response is not 10 then the program will allow a connection to happen the return type will be the Id of which
* the chat person becomes!
*/
// should the method return 0 the Application will do NOTHING!
switch (id) {
case 1:
int k = reciveCommando();
if (k== 10) {
return 10;
}else if (k<= 3) {
return k;
}else {
return 10;
}
/*
* Closes the connection with the server!
*/
case 3:
socket.close();
return 0;
default:
return 0;
}
}
/*
* this method recives a command from the server! the comands can be found in the ChatCommands.txt
* returns the command as an integer!
*/
public int reciveCommando() throws IOException{
Scanner commandoFromServer = new Scanner(socket.getInputStream());
Integer i = Integer.parseInt(commandoFromServer.nextLine());
return i;
}
/**
* Gets a String response from the server. This method i used to create other users and give them the correct username.
*
* @param i
* @return
* @throws IOException
*/
public String getStringResponse(int i) throws IOException {
pw.print(i);
pw.flush();
Scanner commandFromServer = new Scanner(socket.getInputStream());
String x = commandFromServer.nextLine();
return x;
}
}
除此之外我还有一个用作“主要”类的GUI。
我有一个名为SocketTest v3.0.0的程序（如果有人知道的话）它基本上做的是它为我创建了一个可以连接的服务器。
现在我的程序运行并连接到服务器！但是当我尝试在我的客户端程序中调用方法sendCommand或sendChat或任何其他方法（除了连接）之后，它给了我一个nullpointer execption。
我已经将问题缩小到当我声明套接字然后套接字为null时如何解决这个问题？因为我无法在我的Public类下初始化套接字！
我希望你明白我的意思，如果没有请回复，我会详细介绍！
提前谢谢！
答案 0 :(得分：1)
似乎很奇怪“sendCommandO”创建了自己的printwriter而不是使用 全球性的。以后有两个打印机正在喂食，这肯定是在麻烦 相同的流。 “连接”立即发送“连接......”似乎很奇怪。
这个程序的结构通常不会起作用，因为在读者阅读之前，你的写作会阻塞并且无法解锁。它似乎适用于少量数据。读写必须在不同的线程中完成。
这些都不是你当前的问题，但我建议完全改写。
答案 1 :(得分：1)
在插座的使用寿命期间，您必须使用相同的流，扫描仪等。每次要进行I / O时都不会创建新的。否则，您将丢失缓冲区中的数据。
答案 2 :(得分：0)
首先，谢谢你们所有的帮助和回应，这就是我的代码工作的原因：
清除代码以确保每个代码中只有1个已创建，并且这些代码是在客户端连接到服务器时创建的
为了确保我可以在所有方法中同时使用PrintWriter和Scanner，我必须将字段设为静态
感谢您的帮助，我的客户端现在连接到服务器，并能够反复发送消息！ :)
完整的代码来到这里：
import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.util.Scanner;
public class Client {
public final static int portNumber = 6040;
public static Socket socket;
private static PrintWriter pw;
private static Scanner input;
/**
* @param args
* @throws IOException
*/
public static void connect() throws IOException{
// du kan vælge at bruge inetadressen til at connecte i socketet.
InetAddress adr = InetAddress.getByName("localhost");
socket = new Socket("localhost", portNumber);
input=new Scanner(socket.getInputStream());
pw = new PrintWriter(socket.getOutputStream());
pw.println("Connected waiting for input");
pw.flush();
}
/**
* This method sends the message (that the client(chat person) writes to the user)
* @param x
* @throws NullPointerException
* @throws IOException
*/
public void SendChat(String x) throws NullPointerException{
pw.print(x);
pw.flush();
}
public int sendCommando(int id) throws IOException{
pw.print(id);
pw.flush();
/*
* this part of the program sends a command to the server if the command is 1 then 1 is = Connect.
* the program then ask the server is the server is full or is it ok to connect?
* if the response is not 10 then the program will allow a connection to happen the return type will be the Id of which
* the chat person becomes!
*/
// should the method return 0 the Application will do NOTHING!
switch (id) {
case 1:
int k = reciveCommando();
if (k== 10) {
return 10;
}else if (k < 3) {
System.out.println("returned k" + k);
return k;
}else {
return 10;
}
/*
* Closes the connection with the server!
*/
case 3:
socket.close();
return 0;
default:
return 0;
}
}
/*
* this method recives a command from the server! the comands can be found in the ChatCommands.txt
* returns the command as an integer!
*/
public int reciveCommando() throws IOException{
Integer i = input.nextInt();
return i;
}
/**
* Gets a String response from the server. This method i used to create other users and give them the correct username.
*
* @param i
* @return
* @throws IOException
*/
public String getStringResponse(int i) throws IOException {
pw.print(i);
pw.flush();
String x = input.nextLine();
return x;
}
}