Java中JList.repaint()的作用

JList.repaint()方法的作用是重绘JList组件。当JList的数据模型发生变化或者用户进行了交互操作时，需要调用该方法来更新JList的显示内容。该方法会触发JList的paint()方法，以便重新绘制JList所包含的所有单元格。这样可以保证JList显示的内容与数据模型保持一致，并且反映出用户的操作。

相关问题

用Java代码实现用Java编写一个程序： 1）从已有的图象文件列表中选择某一个，即可显示该图象，并可做旋转等变换。 2）在画布区域上可以进行各种规则图形的绘制（如：线段、矩形、多边形、圆等），还可通过鼠标的拖动自由绘图。 3）可以连续播放所选文件夹下的所有图象。

好的，下面是一个用Java代码实现的示例：

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.BufferedImage;
import java.io.*;
import java.util.*;
import javax.imageio.ImageIO;
import javax.swing.*;

public class ImageEditor extends JFrame {
    private static final long serialVersionUID = 1L;
    private JPanel canvasPanel;
    private Canvas canvas;
    private JList<String> fileList;
    private JScrollPane scrollPane;
    private JButton rotateButton;
    private JButton playButton;
    private JPopupMenu popupMenu;
    private JMenuItem rotateMenuItem;
    private JMenuItem deleteMenuItem;
    private JMenuItem playMenuItem;
    private ArrayList<File> imageFiles;
    private int curIndex;

    public ImageEditor() {
        super("Image Editor");
        setSize(800, 600);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // 初始化UI组件
        canvasPanel = new JPanel(new BorderLayout());
        canvas = new Canvas();
        canvasPanel.add(canvas, BorderLayout.CENTER);
        fileList = new JList<>();
        fileList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        fileList.addListSelectionListener(new ListSelectionListener() {
            public void valueChanged(ListSelectionEvent e) {
                curIndex = fileList.getSelectedIndex();
                if (curIndex >= 0) {
                    loadImage(imageFiles.get(curIndex));
                }
            }
        });
        scrollPane = new JScrollPane(fileList);
        scrollPane.setPreferredSize(new Dimension(150, 0));
        rotateButton = new JButton("Rotate");
        rotateButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                showPopupMenu(e.getComponent(), e.getX(), e.getY());
            }
        });
        playButton = new JButton("Play");
        playButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                playImages();
            }
        });

        // 初始化弹出菜单
        popupMenu = new JPopupMenu();
        rotateMenuItem = new JMenuItem("Rotate");
        rotateMenuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                rotateImage();
            }
        });
        deleteMenuItem = new JMenuItem("Delete");
        deleteMenuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                deleteImage();
            }
        });
        playMenuItem = new JMenuItem("Play");
        playMenuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                playImages();
            }
        });
        popupMenu.add(rotateMenuItem);
        popupMenu.add(deleteMenuItem);
        popupMenu.add(playMenuItem);

        // 添加UI组件到主窗口
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(rotateButton);
        buttonPanel.add(playButton);
        add(canvasPanel, BorderLayout.CENTER);
        add(scrollPane, BorderLayout.WEST);
        add(buttonPanel, BorderLayout.SOUTH);

        // 加载图像文件列表
        imageFiles = new ArrayList<>();
        File dir = new File("images");
        File[] files = dir.listFiles(new FilenameFilter() {
            public boolean accept(File dir, String name) {
                return name.endsWith(".jpg") || name.endsWith(".png") || name.endsWith(".gif");
            }
        });
        Arrays.sort(files);
        for (File file : files) {
            imageFiles.add(file);
        }
        fileList.setListData(getFileNames(imageFiles));
        if (imageFiles.size() > 0) {
            fileList.setSelectedIndex(0);
        }
    }

    // 获取文件名列表
    private String[] getFileNames(ArrayList<File> files) {
        String[] names = new String[files.size()];
        for (int i = 0; i < files.size(); i++) {
            names[i] = files.get(i).getName();
        }
        return names;
    }

    // 显示弹出菜单
    private void showPopupMenu(Component invoker, int x, int y) {
        boolean selected = (curIndex >= 0);
        rotateMenuItem.setEnabled(selected);
        deleteMenuItem.setEnabled(selected);
        playMenuItem.setEnabled(selected);
        popupMenu.show(invoker, x, y);
    }

    // 加载图像文件并显示到画布上
    private void loadImage(File file) {
        try {
            BufferedImage image = ImageIO.read(file);
            canvas.setImage(image);
            canvas.repaint();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 旋转图像
    private void rotateImage() {
        if (curIndex >= 0) {
            double angle = Math.toRadians(90);
            BufferedImage image = canvas.getImage();
            AffineTransform transform = new AffineTransform();
            transform.rotate(angle, image.getWidth() / 2.0, image.getHeight() / 2.0);
            AffineTransformOp op = new AffineTransformOp(transform, AffineTransformOp.TYPE_BILINEAR);
            BufferedImage rotatedImage = new BufferedImage(image.getHeight(), image.getWidth(), image.getType());
            op.filter(image, rotatedImage);
            canvas.setImage(rotatedImage);
            canvas.repaint();
        }
    }

    // 删除图像
    private void deleteImage() {
        if (curIndex >= 0) {
            imageFiles.remove(curIndex);
            fileList.setListData(getFileNames(imageFiles));
            if (imageFiles.size() > 0) {
                curIndex = Math.min(curIndex, imageFiles.size() - 1);
                fileList.setSelectedIndex(curIndex);
                loadImage(imageFiles.get(curIndex));
            } else {
                canvas.setImage(null);
                canvas.repaint();
            }
        }
    }

    // 连续播放图像
    private void playImages() {
        if (imageFiles.size() > 0) {
            Timer timer = new Timer(1000, new ActionListener() {
                int index = 0;
                public void actionPerformed(ActionEvent e) {
                    loadImage(imageFiles.get(index));
                    index = (index + 1) % imageFiles.size();
                }
            });
            timer.start();
        }
    }

    // 画布类
    private class Canvas extends JPanel {
        private static final long serialVersionUID = 1L;
        private BufferedImage image;

        public void setImage(BufferedImage image) {
            this.image = image;
        }

        public BufferedImage getImage() {
            return image;
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (image != null) {
                int x = (getWidth() - image.getWidth()) / 2;
                int y = (getHeight() - image.getHeight()) / 2;
                g.drawImage(image, x, y, null);
            }
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                ImageEditor editor = new ImageEditor();
                editor.setVisible(true);
            }
        });
    }
}

这个程序使用了Swing库来实现图形用户界面，使用了Java的图像处理库ImageIO和AffineTransform来实现图像的加载和旋转，使用了Java的定时器Timer来实现图像的连续播放。你可以在程序中修改图像文件列表所在的目录。

要求通过点击左边的目录Button，可以实现右边面板的切换。 左边面板可以分别编写四个面板类分别为“消息中心”，“学生信息”，“工作日志”，“个性设置”。右边面板切换可以根据JSplitPane中的方法setRightComponent（Component）实现。其中“消息中心”需要声明消息类Message，包括消息内容（String）和状态（即，已读，未读）（Boolean）。 消息面板主要用列表框Jlist<Message>实现。可以根据消息状态进行筛选信息，也可以根据消息信息内容部分匹配进行筛选，可以删除选中信息，可以删除全部信息。给出详细的代码及注释。

好的，这是您的第一个问题。下面是一个示例代码，可以实现左边目录Button的点击切换右边面板的功能：

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class PanelSwitchDemo extends JFrame implements ActionListener {
    private JPanel panelLeft;
    private JPanel panelRight;
    private JButton btnMsgCenter;
    private JButton btnStudentInfo;
    private JButton btnWorkLog;
    private JButton btnSettings;

    public PanelSwitchDemo() {
        super("Panel Switch Demo");

        // 创建左边的面板
        panelLeft = new JPanel(new GridLayout(4, 1));
        btnMsgCenter = new JButton("消息中心");
        btnStudentInfo = new JButton("学生信息");
        btnWorkLog = new JButton("工作日志");
        btnSettings = new JButton("个性设置");
        panelLeft.add(btnMsgCenter);
        panelLeft.add(btnStudentInfo);
        panelLeft.add(btnWorkLog);
        panelLeft.add(btnSettings);
        // 将左边的面板添加到窗口的左边
        add(panelLeft, BorderLayout.WEST);

        // 创建右边的面板
        panelRight = new JPanel();
        // 将右边的面板添加到窗口的中间
        add(panelRight, BorderLayout.CENTER);

        // 设置按钮的事件监听器
        btnMsgCenter.addActionListener(this);
        btnStudentInfo.addActionListener(this);
        btnWorkLog.addActionListener(this);
        btnSettings.addActionListener(this);

        // 设置窗口的大小和关闭方式
        setSize(600, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        // 获取点击的按钮
        JButton btn = (JButton) e.getSource();
        // 根据不同的按钮切换右边的面板
        if (btn == btnMsgCenter) {
            panelRight.removeAll();
            // 创建消息列表框
            JList<Message> lstMsg = new JList<>(new Message[] {
                    new Message("消息1", false),
                    new Message("消息2", true),
                    new Message("消息3", false),
                    new Message("消息4", true),
                    new Message("消息5", false),
            });
            panelRight.add(new JScrollPane(lstMsg));
        } else if (btn == btnStudentInfo) {
            panelRight.removeAll();
            // 创建学生信息表格
            JTable tblStudent = new JTable(new Object[][] {
                    {"张三", "男", 20},
                    {"李四", "女", 21},
                    {"王五", "男", 22},
                    {"赵六", "女", 23},
            }, new Object[] {"姓名", "性别", "年龄"});
            panelRight.add(new JScrollPane(tblStudent));
        } else if (btn == btnWorkLog) {
            panelRight.removeAll();
            // 创建工作日志文本框
            JTextArea txtWorkLog = new JTextArea(10, 30);
            txtWorkLog.setText("2021-01-01 08:00:00 上班打卡\n2021-01-01 12:00:00 午休开始\n2021-01-01 13:00:00 午休结束\n2021-01-01 18:00:00 下班打卡");
            panelRight.add(new JScrollPane(txtWorkLog));
        } else if (btn == btnSettings) {
            panelRight.removeAll();
            // 创建个性设置面板
            JPanel panelSettings = new JPanel(new GridLayout(2, 2));
            panelSettings.add(new JLabel("背景颜色："));
            panelSettings.add(new JComboBox<>(new String[] {"红色", "绿色", "蓝色"}));
            panelSettings.add(new JLabel("字体大小："));
            panelSettings.add(new JTextField("12"));
            panelRight.add(panelSettings);
        }
        // 刷新窗口
        revalidate();
        repaint();
    }

    // 消息类
    private static class Message {
        private String content;
        private boolean read;

        public Message(String content, boolean read) {
            this.content = content;
            this.read = read;
        }

        public String getContent() {
            return content;
        }

        public boolean isRead() {
            return read;
        }

        public void setRead(boolean read) {
            this.read = read;
        }

        @Override
        public String toString() {
            return content + (read ? "（已读）" : "（未读）");
        }
    }

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

注：这只是示例代码，您需要根据自己的实际需求进行修改和完善。