我讨厌问一个问题，但是我是爪哇编程的新手……就像昨天一样。我正在尝试将服务器和GUI拼接在一起，但是有这个问题。对不起，再次提出了一个简单的问题。
* Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
import java.awt.*;
import java.awt.event.*;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;
import javax.swing.*;
/*
* The chat client thread. This client thread opens the input and the output
* streams for a particular client, ask the client's name, informs all the
* clients connected to the server about the fact that a new client has joined
* the chat room, and as long as it receive data, echos that data back to all
* other clients. The thread broadcast the incoming messages to all clients and
* routes the private message to the particular client. When a client leaves the
* chat room this thread informs also all the clients about that and terminates.
*/
class clientThread extends Thread {
private String clientName = null;
private DataInputStream is = null;
private PrintStream os = null;
private Socket clientSocket = null;
private final clientThread[] threads;
private int maxClientsCount;
public clientThread(Socket clientSocket, clientThread[] threads) {
this.clientSocket = clientSocket;
this.threads = threads;
maxClientsCount = threads.length;
}
@SuppressWarnings("deprecation")
public void run() {
int maxClientsCount = this.maxClientsCount;
clientThread[] threads = this.threads;
try {
/*
* Create input and output streams for this client.
*/
is = new DataInputStream(clientSocket.getInputStream());
os = new PrintStream(clientSocket.getOutputStream());
String name;
while (true) {
os.println("Enter your name.");
name = is.readLine().trim();
if (name.indexOf('@') == -1) {
break;
} else {
os.println("The name should not contain '@' character.");
}
}
/* Welcome the new the client. */
os.println("Welcome " + name
+ " to our chat room.nTo leave enter /quit in a new line.");
synchronized (this) {
for (int i = 0; i < maxClientsCount; i++) {
if (threads[i] != null && threads[i] == this) {
clientName = "@" + name;
break;
}
}
for (int i = 0; i < maxClientsCount; i++) {
if (threads[i] != null && threads[i] != this) {
threads[i].os.println("*** A new user " + name
+ " entered the chat room !!! ***");
}
}
}
/* Start the conversation. */
while (true) {
String line = is.readLine();
if (line.startsWith("/quit")) {
break;
}
/* If the message is private sent it to the given client. */
if (line.startsWith("@")) {
String[] words = line.split("\s", 2);
if (words.length > 1 && words[1] != null) {
words[1] = words[1].trim();
if (!words[1].isEmpty()) {
synchronized (this) {
for (int i = 0; i < maxClientsCount; i++) {
if (threads[i] != null && threads[i] != this
&& threads[i].clientName != null
&& threads[i].clientName.equals(words[0])) {
threads[i].os.println("<" + name + "> " + words[1]);
/*
* Echo this message to let the client know the private
* message was sent.
*/
this.os.println(">" + name + "> " + words[1]);
break;
}
}
}
}
}
} else {
/* The message is public, broadcast it to all other clients. */
synchronized (this) {
for (int i = 0; i < maxClientsCount; i++) {
if (threads[i] != null && threads[i].clientName != null) {
threads[i].os.println("<" + name + "> " + line);
}
}
}
}
}
synchronized (this) {
for (int i = 0; i < maxClientsCount; i++) {
if (threads[i] != null && threads[i] != this
&& threads[i].clientName != null) {
threads[i].os.println("*** The user " + name
+ " is leaving the chat room !!! ***");
}
}
}
os.println("*** Bye " + name + " ***");
/*
* Clean up. Set the current thread variable to null so that a new client
* could be accepted by the server.
*/
synchronized (this) {
for (int i = 0; i < maxClientsCount; i++) {
if (threads[i] == this) {
threads[i] = null;
}
}
}
/*
* Close the output stream, close the input stream, close the socket.
*/
is.close();
os.close();
clientSocket.close();
} catch (IOException e) {
}
}
}
/*
* A chat server that delivers public and private messages.
*/
class DynamicWrite {
// The server socket.
private static ServerSocket serverSocket = null;
// The client socket.
private static Socket clientSocket = null;
// This chat server can accept up to maxClientsCount clients' connections.
private static final int maxClientsCount = 10;
private static final clientThread[] threads = new clientThread[maxClientsCount];
static void start(int args) {
// The default port number.
int portNumber = 5556;
TextDemo.textArea.append("Now using port 5556");
//Make sure the new text is visible, even if there
//was a selection in the text area.
TextDemo.textArea.setCaretPosition(TextDemo.textArea.getDocument().getLength());
/*
* Open a server socket on the portNumber (default 2222). Note that we can
* not choose a port less than 1023 if we are not privileged users (root).
*/
try {
serverSocket = new ServerSocket(portNumber);
} catch (IOException e) {
System.out.println(e);
}
/*
* Create a client socket for each connection and pass it to a new client
* thread.
*/
while (true) {
try {
clientSocket = serverSocket.accept();
int i = 0;
for (i = 0; i < maxClientsCount; i++) {
if (threads[i] == null) {
(threads[i] = new clientThread(clientSocket, threads)).start();
break;
}
}
if (i == maxClientsCount) {
PrintStream os = new PrintStream(clientSocket.getOutputStream());
os.println("Server too busy. Try later.");
os.close();
clientSocket.close();
}
} catch (IOException e) {
System.out.println(e);
}
}
}
}
@SuppressWarnings("serial")
public class TextDemo extends JPanel {
static JTextArea textArea;
final static String newline = "n";
public TextDemo() {
super(new GridBagLayout());
textArea = new JTextArea(5, 20);
textArea.setEditable(false);
JScrollPane scrollPane = new JScrollPane(textArea);
//Add Components to this panel.
GridBagConstraints c = new GridBagConstraints();
c.gridwidth = GridBagConstraints.REMAINDER;
c.fill = GridBagConstraints.HORIZONTAL;
c.fill = GridBagConstraints.BOTH;
c.weightx = 1.0;
c.weighty = 1.0;
add(scrollPane, c);
JPanel panel = new JPanel();
scrollPane.setColumnHeaderView(panel);
JButton btnTest = new JButton("Test");
btnTest.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
textArea.append("Yuup" + newline);
//Make sure the new text is visible, even if there
//was a selection in the text area.
textArea.setCaretPosition(textArea.getDocument().getLength());
}
});
panel.add(btnTest);
}
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event dispatch thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("TextDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Add contents to the window.
frame.getContentPane().add(new TextDemo());
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event dispatch thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
DynamicWrite.start(5556);
}
}
这样就这样了。我被扔了
Exception in thread "main" java.lang.NullPointerException
at DynamicWrite.start(TextDemo.java:203)
at TextDemo.main(TextDemo.java:311)"
每当我尝试运行它时。而且我一生无法找到这个问题。我知道我有很多东西要学习。谢谢，〜P
我假设您忘了初始化变量，因为这是null指针异常的常见情况。快速查看您的代码，我认为它在TextDemo下。可能是static JTextArea textArea = new JTextArea();。
检查此部分。
@SuppressWarnings("deprecation")
public void run() {
int maxClientsCount = this.maxClientsCount;
clientThread[] threads = this.threads;
您已经声明了此2。检查一下并告诉我它是否有效。