用Java图形界面的知识，编写以下软件：点击read按钮，则读入指定txt文档中的内容，显示在左边文本域中，点击sort按钮，则将文本域中以“DBa”开头的字符串提取出来，放到右边的文本域中，点击save按钮，则将处理过后右边的文本保存到一个新的txt文档中。该代码需要注释

好的，以下是一个示例的Java图形界面程序，可以实现您所描述的功能。代码中有详细的注释，您可以根据自己的需求进行修改。

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.border.EmptyBorder;

public class TxtFileSorter extends JFrame {

    private JPanel contentPane;
    private JTextArea textAreaLeft;
    private JTextArea textAreaRight;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    TxtFileSorter frame = new TxtFileSorter();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public TxtFileSorter() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 640, 480);
        setTitle("Txt File Sorter");

        // 创建主面板
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        // 创建左边的文本域和滚动条
        JScrollPane scrollPaneLeft = new JScrollPane();
        scrollPaneLeft.setBounds(10, 42, 300, 380);
        contentPane.add(scrollPaneLeft);

        textAreaLeft = new JTextArea();
        scrollPaneLeft.setViewportView(textAreaLeft);

        // 创建右边的文本域和滚动条
        JScrollPane scrollPaneRight = new JScrollPane();
        scrollPaneRight.setBounds(320, 42, 300, 380);
        contentPane.add(scrollPaneRight);

        textAreaRight = new JTextArea();
        scrollPaneRight.setViewportView(textAreaRight);

        // 创建read按钮
        JButton btnRead = new JButton("read");
        btnRead.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                // 选择txt文件
                JFileChooser fileChooser = new JFileChooser();
                fileChooser.setCurrentDirectory(new File("."));
                int result = fileChooser.showOpenDialog(TxtFileSorter.this);
                if (result == JFileChooser.APPROVE_OPTION) {
                    File selectedFile = fileChooser.getSelectedFile();

                    // 读取txt文件
                    try (BufferedReader reader = new BufferedReader(new FileReader(selectedFile))) {
                        String line = null;
                        StringBuilder sb = new StringBuilder();
                        while ((line = reader.readLine()) != null) {
                            sb.append(line);
                            sb.append(System.lineSeparator());
                        }
                        textAreaLeft.setText(sb.toString());
                    } catch (IOException ex) {
                        ex.printStackTrace();
                    }
                }
            }
        });
        btnRead.setBounds(10, 10, 80, 22);
        contentPane.add(btnRead);

        // 创建sort按钮
        JButton btnSort = new JButton("sort");
        btnSort.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                // 获取左边文本域的内容
                String text = textAreaLeft.getText();

                // 将以"DBa"开头的字符串提取出来
                StringBuilder sb = new StringBuilder();
                String[] lines = text.split(System.lineSeparator());
                for (String line : lines) {
                    if (line.startsWith("DBa")) {
                        sb.append(line);
                        sb.append(System.lineSeparator());
                    }
                }

                // 将结果显示在右边的文本域中
                textAreaRight.setText(sb.toString());
            }
        });
        btnSort.setBounds(100, 10, 80, 22);
        contentPane.add(btnSort);

        // 创建save按钮
        JButton btnSave = new JButton("save");
        btnSave.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                // 选择保存的文件路径
                JFileChooser fileChooser = new JFileChooser();
                fileChooser.setCurrentDirectory(new File("."));
                int result = fileChooser.showSaveDialog(TxtFileSorter.this);
                if (result == JFileChooser.APPROVE_OPTION) {
                    File selectedFile = fileChooser.getSelectedFile();

                    // 将右边文本域的内容保存到文件中
                    try (BufferedWriter writer = new BufferedWriter(new FileWriter(selectedFile))) {
                        writer.write(textAreaRight.getText());
                    } catch (IOException ex) {
                        ex.printStackTrace();
                    }
                }
            }
        });
        btnSave.setBounds(190, 10, 80, 22);
        contentPane.add(btnSave);

        // 创建左边的文本域标签
        JLabel lblLeft = new JLabel("Left:");
        lblLeft.setBounds(10, 25, 80, 15);
        contentPane.add(lblLeft);

        // 创建右边的文本域标签
        JLabel lblRight = new JLabel("Right:");
        lblRight.setBounds(320, 25, 80, 15);
        contentPane.add(lblRight);
    }
}