以下错误是通过删除声明来修复的，但另一个已经出现以前不存在。
收到两个错误，任何见解都会很棒，谢谢。
线程“main”java.lang.NullPointerException中的异常 在ChatClient。（ChatClient.java:27） 在ChatClient.main（ChatClient.java:59）
来自以下ChatClient：
import java.net.*;
import java.io.*;
public class ChatClient
{ private Socket socket = null;
private BufferedReader console = null;
private BufferedReader streamIn = null;
private DataOutputStream streamOut = null;
public ChatClient(String serverName, int serverPort, String userName)
{ System.out.println("Establishing connection. Please wait...");
try
{ socket = new Socket(serverName, serverPort);
System.out.println("Connected: " + socket);
System.out.println("CTRL+C or type .bye to quit");
start();
}
catch(UnknownHostException uhe)
{ System.out.println("Host unknown: " + uhe.getMessage());
}
catch(IOException ioe)
{ System.out.println("Unexpected exception: " + ioe.getMessage());
}
String line = "";
while (!line.equals(".bye"))
{ try
{ line = console.readLine();
streamOut.writeBytes(line + '\n'); //Send console data to server socket
String reply = streamIn.readLine(); //Recieve confirmation msg from server
System.out.println( reply ); //Print the msg
streamOut.flush();
}
catch(IOException ioe)
{ System.out.println("Sending error: " + ioe.getMessage());
}
}
}
public void start() throws IOException
{ console = new BufferedReader(new InputStreamReader(System.in)); //Changed console to BufferedReader
streamIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
streamOut = new DataOutputStream(socket.getOutputStream());
}
public void stop()
{ try
{ if (console != null) console.close();
if (streamOut != null) streamOut.close();
if (streamIn != null) streamIn.close(); //Is it good practice to close
if (socket != null) socket.close();
}
catch(IOException ioe)
{ System.out.println("Error closing ...");
}
}
public static void main(String args[])
{ ChatClient client = null;
if (args.length != 3)
System.out.println("Usage: java ChatClient host port username");
else
client = new ChatClient(args[0], Integer.parseInt(args[1]), args[2]);
}
}
并出现此错误：
Exception in thread "Thread-1" java.lang.NullPointerException
at ChatServerThread.handleClient(ChatServerThread.java:41)
at ChatServerThread.run(ChatServerThread.java:17)
：
import java.net.*;
import java.io.*;
//public class ChatServerThread implements Runnable
public class ChatServerThread extends Thread
{ private Socket socket = null;
private ChatServer server = null;
private int ID = -1;
private BufferedReader streamIn = null;
private DataOutputStream streamOut = null;
public ChatServerThread(ChatServer _server, Socket _socket)
{ server = _server; socket = _socket; ID = socket.getPort();
}
public void run() {
try {
handleClient();
} catch( EOFException eof ) {
System.out.println("Client closed the connection.");
} catch( IOException ioe ) {
ioe.printStackTrace();
}
}
public void handleClient() throws IOException {
boolean done = false;
try {
System.out.println("Server Thread " + ID + " running.");
while (!done) {
String nextCommand = streamIn.readLine();
if( nextCommand.equals(".bye") ) {
System.out.println("Client disconnected with bye.");
done = true;
} else {
System.out.println( nextCommand );
String nextReply = "You sent me: " + nextCommand.toUpperCase() + '\n';
streamOut.writeBytes ( nextReply );
}
}
} finally {
streamIn.close();
streamOut.close();
socket.close();
}
}
public void open() throws IOException
{
streamIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
streamOut = new DataOutputStream(socket.getOutputStream());
}
public void close() throws IOException
{ if (socket != null) socket.close();
if (streamIn != null) streamIn.close();
if (streamOut != null) streamOut.close();
}
}
答案 0 :(得分：3)
是的，就是这一行：
line = console.readLine();
console仍然为空。即使你正在调用start()，它也不会按照你的想法行事：
public void start() throws IOException
{ BufferedReader console = new BufferedReader(new InputStreamReader(System.in));
这声明了一个名为console的新本地变量。它不会更改名为console的实例变量的值。为此，您应该删除声明部分：
public void start() throws IOException
{
console = new BufferedReader(new InputStreamReader(System.in));
...
即使有了这样的改变，你也可能会遇到问题 - 因为如果那个 会抛出一个异常，那么你在构造函数中用它做的就是：
catch(IOException ioe)
{ System.out.println("Unexpected exception: " + ioe.getMessage());
}
然后你继续好像什么也没发生过一样。不要那样做。你并没有真正“处理”异常 - 所以你几乎肯定要么首先不抓住它，要么在你的catch块中重新抛出它。
顺便说一句，你的支撑风格非常密集，非传统和不一致。我会强烈建议不要在开头括号后面包含代码（在同一行）。事实上，对于任何习惯于（非常）更常见的约定的人来说，你的代码都很难阅读：
if (foo) {
// Do something
}
或
if (foo)
{
// Do something
}
答案 1 :(得分：1)
对于第一个例外，永远不会为console分配一个对象，因此您无法在其上调用方法：
line = console.readLine();
// ^ still null
同样，对于第二个例外，
streamIn.close();
// ^ streamIn is still null
问题在于重新陈述start()中变量的类型。这实际上创建了 new 变量，这些变量仅对该方法是本地的，并且不引用同名的全局变量。
答案 2 :(得分：1)
现在它应该运行客户端
public void start() throws IOException
{ console = new BufferedReader(new InputStreamReader(System.in)); //Changed console to BufferedReader
streamIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
streamOut = new DataOutputStream(socket.getOutputStream());
}
答案 3 :(得分：1)
在你的开始方法
public void start() throws IOException
{ BufferedReader console = new BufferedReader(new InputStreamReader(System.in)); //Changed console to BufferedReader
BufferedReader streamIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
DataOutputStream streamOut = new DataOutputStream(socket.getOutputStream());
}
您声明了新的本地变量，而不是像我想的那样，分配您已声明的实例变量。如果将其更改为
public void start() throws IOException
{ console = new BufferedReader(new InputStreamReader(System.in)); //Changed console to BufferedReader
streamIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
streamOut = new DataOutputStream(socket.getOutputStream());
}
应该有效
您在第二堂课的open()方法中犯了同样的错误
答案 4 :(得分：1)
这是因为，控制台为空。要解决此问题，请将start();方法修改为：
public void start() throws IOException
{
console = new BufferedReader(new InputStreamReader(System.in));
streamIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
streamOut = new DataOutputStream(socket.getOutputStream());
}