为我提供Java代码要求1. 编写图形用户界面，教师为服务器端，学生为客户端，一个服务端可以接受多个客户端连接。 2. 要求完成教师白板的建立,实现教师在白板上画图，学生端能够实时刷新。 3. 教师可以传输文件给学生。 4. 学生可以向教师提问，问答内容所有学生都能看到。

好的，以下是Java代码示例：

教师端代码：

import java.io.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Teacher extends JFrame implements ActionListener {
    private ServerSocket serverSocket;
    private ArrayList<Socket> clientSockets;
    private ArrayList<ObjectOutputStream> outputStreams;
    private JPanel whiteboard;
    private JButton clearBtn, sendBtn;
    private JTextArea chatArea;
    private JScrollPane chatScrollPane;
    private JTextField chatField;
    private JFileChooser fileChooser;

    public Teacher() {
        setTitle("Teacher");
        setSize(600, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // 初始化界面组件
        whiteboard = new JPanel();
        clearBtn = new JButton("Clear");
        sendBtn = new JButton("Send");
        chatArea = new JTextArea();
        chatScrollPane = new JScrollPane(chatArea);
        chatField = new JTextField();
        fileChooser = new JFileChooser();

        whiteboard.setBackground(Color.WHITE);
        whiteboard.addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                // 绘制图形
            }
        });
        clearBtn.addActionListener(this);
        sendBtn.addActionListener(this);

        JPanel buttonPanel = new JPanel();
        buttonPanel.add(clearBtn);
        buttonPanel.add(sendBtn);

        JPanel chatPanel = new JPanel(new BorderLayout());
        chatPanel.add(chatScrollPane, BorderLayout.CENTER);
        chatPanel.add(chatField, BorderLayout.SOUTH);

        add(whiteboard, BorderLayout.CENTER);
        add(buttonPanel, BorderLayout.NORTH);
        add(chatPanel, BorderLayout.SOUTH);

        setVisible(true);

        // 初始化服务器
        try {
            serverSocket = new ServerSocket(9999);
            clientSockets = new ArrayList<Socket>();
            outputStreams = new ArrayList<ObjectOutputStream>();

            while (true) {
                Socket socket = serverSocket.accept();
                clientSockets.add(socket);
                ObjectOutputStream outputStream = new ObjectOutputStream(socket.getOutputStream());
                outputStreams.add(outputStream);

                // 启动客户端线程
                new ClientThread(socket).start();
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    // 处理按钮事件
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == clearBtn) {
            // 清空白板
        } else if (e.getSource() == sendBtn) {
            // 发送消息
            String message = chatField.getText();
            chatArea.append("Teacher: " + message + "\n");
            broadcastMessage("Teacher: " + message);
            chatField.setText("");
        }
    }

    // 广播消息给所有客户端
    private void broadcastMessage(String message) {
        for (ObjectOutputStream outputStream : outputStreams) {
            try {
                outputStream.writeObject(message);
                outputStream.flush();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }

    // 处理客户端消息的线程
    private class ClientThread extends Thread {
        private Socket socket;
        private ObjectInputStream inputStream;

        public ClientThread(Socket socket) throws IOException {
            this.socket = socket;
            inputStream = new ObjectInputStream(socket.getInputStream());
        }

        public void run() {
            try {
                while (true) {
                    String message = (String) inputStream.readObject();
                    chatArea.append(message + "\n");
                    broadcastMessage(message);
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            } catch (ClassNotFoundException ex) {
                ex.printStackTrace();
            } finally {
                try {
                    inputStream.close();
                    socket.close();
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        new Teacher();
    }
}

学生端代码：

import java.io.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Student extends JFrame implements ActionListener {
    private Socket socket;
    private ObjectOutputStream outputStream;
    private ObjectInputStream inputStream;
    private JPanel whiteboard;
    private JTextArea chatArea;
    private JScrollPane chatScrollPane;
    private JTextField chatField;
    private JButton sendBtn, fileBtn;

    public Student() {
        setTitle("Student");
        setSize(600, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // 初始化界面组件
        whiteboard = new JPanel();
        chatArea = new JTextArea();
        chatScrollPane = new JScrollPane(chatArea);
        chatField = new JTextField();
        sendBtn = new JButton("Send");
        fileBtn = new JButton("File");

        whiteboard.setBackground(Color.WHITE);
        chatArea.setEditable(false);
        sendBtn.addActionListener(this);
        fileBtn.addActionListener(this);

        JPanel buttonPanel = new JPanel();
        buttonPanel.add(sendBtn);
        buttonPanel.add(fileBtn);

        JPanel chatPanel = new JPanel(new BorderLayout());
        chatPanel.add(chatScrollPane, BorderLayout.CENTER);
        chatPanel.add(chatField, BorderLayout.SOUTH);

        add(whiteboard, BorderLayout.CENTER);
        add(buttonPanel, BorderLayout.NORTH);
        add(chatPanel, BorderLayout.SOUTH);

        setVisible(true);

        // 连接服务器
        try {
            socket = new Socket("localhost", 9999);
            outputStream = new ObjectOutputStream(socket.getOutputStream());
            inputStream = new ObjectInputStream(socket.getInputStream());

            // 启动接收消息线程
            new ReceiveThread().start();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    // 处理按钮事件
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == sendBtn) {
            // 发送消息
            String message = chatField.getText();
            chatArea.append("Student: " + message + "\n");
            sendMessage("Student: " + message);
            chatField.setText("");
        } else if (e.getSource() == fileBtn) {
            // 发送文件
            int result = fileChooser.showOpenDialog(this);
            if (result == JFileChooser.APPROVE_OPTION) {
                File file = fileChooser.getSelectedFile();
                sendFile(file);
            }
        }
    }

    // 发送消息
    private void sendMessage(String message) {
        try {
            outputStream.writeObject(message);
            outputStream.flush();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    // 发送文件
    private void sendFile(File file) {
        try {
            FileInputStream fileInputStream = new FileInputStream(file);
            byte[] buffer = new byte[1024];
            int length;
            while ((length = fileInputStream.read(buffer)) > 0) {
                outputStream.write(buffer, 0, length);
                outputStream.flush();
            }
            fileInputStream.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    // 接收消息的线程
    private class ReceiveThread extends Thread {
        public void run() {
            try {
                while (true) {
                    Object message = inputStream.readObject();
                    if (message instanceof String) {
                        chatArea.append((String) message + "\n");
                    } else if (message instanceof byte[]) {
                        // 接收文件
                        byte[] buffer = (byte[]) message;
                        FileOutputStream fileOutputStream = new FileOutputStream("file.txt");
                        fileOutputStream.write(buffer);
                        fileOutputStream.close();
                    }
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            } catch (ClassNotFoundException ex) {
                ex.printStackTrace();
            } finally {
                try {
                    inputStream.close();
                    outputStream.close();
                    socket.close();
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        new Student();
    }
}

这里只是提供了一个简单的代码示例，具体细节需要您自己根据需求进行实现。