JLabels 和 TextFields 在单独 method/class 中声明时不出现

Question

我在使 JLabel 和 textFields 出现在 JPanel 上时遇到了一些问题。如果我将所有这些代码放在主要方法中，它就可以正常工作，但是当我将 JLabel 和 TextFields 移到它们自己的方法中或类时，JPanel 仍然是空的。显示的是我使用的图像。

package gui;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.ImageIcon;
import javax.swing.JPanel;

@SuppressWarnings("serial")
class ImagePanel extends JPanel {

    private Image img;

    public ImagePanel(String img) {
        this(new ImageIcon(img).getImage());
    }

    public ImagePanel(Image img) {
        this.img = img;
        Dimension size = new Dimension(img.getWidth(null), img.getHeight(null));
        setPreferredSize(size);
        setMinimumSize(size);
        setMaximumSize(size);
        setSize(size);
        setLayout(null);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(img,  0,  0,  null);
    }
}

public class EquippedInput {

    private JPanel panel;

    public static void main(String[] args){
        ImagePanel panel = new ImagePanel(new ImageIcon("Images/Crusader Background.jpg").getImage());
        JScrollPane scrollBar = new JScrollPane(panel,
                JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        panel.setLayout(null);
        JFrame frame = new JFrame();
        frame.getContentPane().add(scrollBar);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(1160, 1000);
        frame.setVisible(true);
        panel.setPreferredSize(new Dimension(1125, 1210));
        scrollBar.getVerticalScrollBar().setUnitIncrement(20);
    }

    public EquippedInput() {
        initialize();
    }

    private void initialize() {

        /**
         * Stats and slots labels.
         */
        JLabel lblWeaponAttacksPerSecond = new JLabel("Weapon Attacks Per Second");
        JLabel lblWeaponAttackSpeed = new JLabel("Attack Speed");
        JLabel lblMainHand = new JLabel("Main Hand");
        JLabel lblOffHand = new JLabel("Off Hand");

        JLabel stats[] = {lblWeaponAttacksPerSecond, lblWeaponAttackSpeed};
        JLabel slots[] = {lblMainHand, lblOffHand};

        /**
         * Place stats and slots labels.
         */
        for (int i = 0; i < stats.length; i++) {
            stats[i].setBounds(10, (40 + 30 * i), 200, 20);
            panel.add(stats[i]);
        }
        for (int i = 0; i < slots.length; i++) {
            slots[i].setBounds((220 +  70 * i), 10, 60, 20);
            panel.add(slots[i]);
        }

        /**
         * Text fields.
         */
        JTextField textField0 = new JTextField();
        JTextField textField1 = new JTextField();

        JTextField mainHandTextField[] = {textField0, textField1};

        /**
         * Arrays of whether a stat can roll on an item. 1 = can roll. 0 = can't roll.
         */
        int mainHandAvailableStats[] =  {0, 1};

        /**
         * Text field builders, each loop is a single slot.
         */
        for (int i = 0; i < mainHandTextField.length; i++) {
            panel.add(mainHandTextField[i]);
            if(mainHandAvailableStats[i] == 1) {
                int textFieldVerticalPosition = 40 + 30 * i;
                mainHandTextField[i].setBounds(220, textFieldVerticalPosition, 60, 20);
                panel.add(mainHandTextField[i]);
            }
        }
    }
}

JPanel 的实际代码包含更多内容，但这会产生完全相同的结果。

Answer 1

稍后我将不得不解释这段代码和这个答案，但它显示：

从文本文件获取数据并从中创建 table 模型
创建并显示带有不透明空单元格的 JTable
在 JPanel 中显示背景图像

数据文件是这样的：

                        Main_Hand       Off_Hand        Head            Shoulder        Neck
Weapon_Attacks_per_sec  5               null            null            null            null 
Attack_Speed            20              null            null            null            null
Damage_%                30              null            null            null            null
Min_Bonus_Damage        3               null            null            null            null
Max_Bonus_Damage        40              null            null            null            null
Min_Weapon_Damage       30              null            null            null            null
Max_Weapon_Damage       80              null            null            null            null
Strength                70              50              20              30              30

它必须命名为 TableFunData.txt 并且与代码所在的 directory/package 相同。

密码是：

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.Scanner;
import java.util.Vector;

import javax.imageio.ImageIO;
import javax.swing.*;
import javax.swing.table.DefaultTableCellRenderer;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableModel;

@SuppressWarnings("serial")
public class TableFun extends JPanel {
    private static final String IMG_PATH = "https://upload.wikimedia.org/"
            + "wikipedia/commons/d/d1/Ozanne-Brest.jpg";
    private JTable table = new JTable();
    private BufferedImage img;

    public TableFun(BufferedImage img, TableModel model) {
        this.img = img;
        table = new JTable(model);
        table.setDefaultRenderer(Object.class, new MyCellRenderer());
        table.setOpaque(false);
        table.setPreferredScrollableViewportSize(table.getPreferredSize());
        table.setShowGrid(false);
        JScrollPane scrollPane = new JScrollPane(table);
        scrollPane.setOpaque(false);
        scrollPane.getViewport().setOpaque(false);

        setLayout(new BorderLayout());
        add(scrollPane, BorderLayout.CENTER);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (img != null) {
            g.drawImage(img, 0, 0, this);
        }
    }

    @Override
    public Dimension getPreferredSize() {
        Dimension superSize = super.getPreferredSize();
        if (isPreferredSizeSet() || img == null) {
            return superSize;
        }
        int supW = superSize.width;
        int supH = superSize.height;
        int imgW = img.getWidth();
        int imgH = img.getHeight();
        int w = Math.max(imgW, supW);
        int h = Math.max(imgH, supH);
        return new Dimension(w, h);
    }

    private class MyCellRenderer extends DefaultTableCellRenderer {
        @Override
        public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus,
                int row, int column) {
            DefaultTableCellRenderer renderer = (DefaultTableCellRenderer) super.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column);
            if (column != 0) {
                renderer.setHorizontalAlignment(JLabel.CENTER);
            } else {
                renderer.setHorizontalAlignment(JLabel.LEADING);
            }
            renderer.setOpaque(value != null);
            return renderer;
        }
    }

    private static void createAndShowGui() {
        BufferedImage img = null;
        try {
            URL imageUrl = new URL(IMG_PATH);
            img = ImageIO.read(imageUrl);
        } catch (IOException e1) {
            e1.printStackTrace();
            System.exit(-1);
        }
        String dataPath = "TableFunData.txt";
        DataIO dataIO = new DataIO(dataPath);
        TableModel model = null;
        try {
            model = dataIO.createTableModel();
        } catch (IOException e) {
            e.printStackTrace();
            System.exit(-1);
        }

        JFrame frame = new JFrame("Table Fun");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new TableFun(img, model));
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }


    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

class DataIO {

    private static final String NULL = "null";
    private String dataPath;

    public DataIO(String dataPath) {
        this.dataPath = dataPath;
    }

    public TableModel createTableModel() throws IOException {
        InputStream inputStream = getClass().getResourceAsStream(dataPath);
        Scanner scanner = new Scanner(inputStream);
        Vector<String> columnNames = new Vector<>();
        Vector<Vector<Object>> data = new Vector<>();

        while (scanner.hasNext()) {
            String line = scanner.nextLine();
            if (columnNames.size() == 0) {
                columnNames = createColumnNames(line);
            } else {
                Vector<Object> dataRow = createDataRow(line);
                data.add(dataRow);
            }
        }
        if (scanner != null) {
            scanner.close();
        }
        DefaultTableModel model = new DefaultTableModel(data, columnNames);
        return model;
    }

    private Vector<String> createColumnNames(String line) {
        String[] tokens = line.split("\s+");
        Vector<String> columnNames = new Vector<>();
        columnNames.add(" "); // first name is blank
        for (String token : tokens) {
            if (!token.trim().isEmpty()) {
                token = token.replace("_", " "); // add spaces
                columnNames.add(token);
            }
        }
        return columnNames;
    }

    private Vector<Object> createDataRow(String line) {
        String[] tokens = line.split("\s+");
        Vector<Object> dataRow = new Vector<>();
        for (String token : tokens) {
            token = token.trim();
            if (!token.isEmpty()) {
                // first token is the title
                if (dataRow.size() == 0) {
                    token = token.replace("_", " "); // add spaces
                    dataRow.add(token);
                } else {
                    // if title already added
                    if (token.equalsIgnoreCase(NULL)) {
                        dataRow.add(null);
                    } else {
                        int value = Integer.parseInt(token);
                        dataRow.add(value);
                    }
                }
            }
        }
        return dataRow;
    }

}

GUI 看起来像：

现在进行一些解释：

好的，这段代码的作用：

首先，我使用了一个外部图像，可以从维基百科/维基媒体免费获得，这样我的代码就可以从任何计算机运行并演示图像在 JPanel 中的使用。图片路径可以在这里找到：

private static final String IMG_PATH = "https://upload.wikimedia.org/"
        + "wikipedia/commons/d/d1/Ozanne-Brest.jpg";

此处用于创建图像：

        URL imageUrl = new URL(IMG_PATH);
        img = ImageIO.read(imageUrl);

然后在 JPanel 的 paintComponent 方法中绘制：

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    if (img != null) {
        g.drawImage(img, 0, 0, this);
    }
}

我的代码还扩展了 JPanel，因为这为我的 GUI 程序提供了比扩展 JFrame 时更大的灵活性：

public class TableFun extends JPanel {

我重写了 JPanel 的 getPreferredSize 方法，使其大小适合图像，除非它需要更大。这就是为什么我首先获得 super 的首选大小，并尝试使我的 GUI 足够大以显示图像，如果需要显示更多组件则更大：

@Override
public Dimension getPreferredSize() {
    Dimension superSize = super.getPreferredSize();
    if (isPreferredSizeSet() || img == null) {
        return superSize;
    }
    int supW = superSize.width;
    int supH = superSize.height;
    int imgW = img.getWidth();
    int imgH = img.getHeight();
    int w = Math.max(imgW, supW);
    int h = Math.max(imgH, supH);
    return new Dimension(w, h);
}

为了简化代码，我尝试将代码与数据分开，并将我的数据放在一个文本文件中。 DataIO class 是一个小型实用程序 class，用于读取文件中保存的文本，然后逐行解析数据以创建并填充 DefaultTableModel 对象。请注意，我获取的文件不是 "File" 而是 class 资源，因为如果我愿意，这样我可以将它包含在 jar 文件中。我使用扫描仪读取每一行，就像您读取文本文件一样。

public TableModel createTableModel() throws IOException {
    InputStream inputStream = getClass().getResourceAsStream(dataPath);
    Scanner scanner = new Scanner(inputStream);

一旦我得到一行文本，我将它分成白色 space，这将创建一个字符串数组，所有白色 space 都被修剪掉：

String[] tokens = line.split("\s+");

JTable 使用名为 MyCellRenderer table 的单元格渲染器

table.setDefaultRenderer(Object.class, new MyCellRenderer());

如果单元格包含数据，则单元格不透明，如果单元格包含空值，则单元格不透明（透明）:

renderer.setOpaque(value != null);

我还要确保 JTable 本身、JScrollPane 和滚动窗格的视口都是非不透明的，这样图像才能显示出来：

    table.setOpaque(false);

    // ....

    scrollPane.setOpaque(false);
    scrollPane.getViewport().setOpaque(false);

您提到抛出 NPE，这可能意味着您的 Java 程序没有找到文本文件。同样，它必须与您的 class 文件放在一起。您应该使用 Eclipse 在与 java 文件 相同的目录中创建一个文本文件，准确命名为 TableFunData.txt（拼写和大小写很重要），完成后，Eclipse 应该类似于：

使用 Eclipse 的包资源管理器可以在同一个包中看到代码和数据文本（以蓝色和红色突出显示），并且代码的包语句应该表明它实际上位于该包中（以绿色显示）。

Answer 2

这是 JTable 的一个简单实现，正如@Hovercraft Full Of Eels 所建议的那样。背景颜色是根据数据渲染的。 1 将导致背景颜色为蓝色，而 0 将呈现为红色。（演示基于 https://docs.oracle.com/javase/tutorial/displayCode.html?code=https://docs.oracle.com/javase/tutorial/uiswing/examples/components/SimpleTableDemoProject/src/components/SimpleTableDemo.java ）

public class TableDemo extends JPanel {

    public TableDemo() {
        super(new GridLayout(1,0));

        String[] columnNames = {"         ",
                "Main Hand",
                "Off Hand",
                "Head",
                "Shoulder",
        "Neck"};

        Object[][] data = {
                {"Weapon Attacks Per Second", new Integer(1), new Integer(0), new Integer(0),new Integer(0),new Integer(0)},
                {"Attack Speed", new Integer(1), new Integer(0), new Integer(1),new Integer(0),new Integer(0)},
                {"Damage%", new Integer(1), new Integer(0), new Integer(0),new Integer(0),new Integer(0)},
                {"Min Bonus Damage", new Integer(1), new Integer(0), new Integer(0),new Integer(1),new Integer(0)},
                {"Max Bonus Damage", new Integer(1), new Integer(1), new Integer(0),new Integer(0),new Integer(0)},
                {"Min Weapon Damage", new Integer(1), new Integer(0), new Integer(0),new Integer(1),new Integer(0)},
                {"Max Weapon Damage", new Integer(1), new Integer(0), new Integer(1),new Integer(0),new Integer(0)},
        };

        final JTable table = new JTable(data, columnNames);
        table.setPreferredScrollableViewportSize(new Dimension(600, 70));


        table.getColumnModel().getColumn(1).setCellRenderer(new ColorRenderer());
        table.getColumnModel().getColumn(2).setCellRenderer(new ColorRenderer());
        table.getColumnModel().getColumn(3).setCellRenderer(new ColorRenderer());
        table.getColumnModel().getColumn(4).setCellRenderer(new ColorRenderer());
        table.getColumnModel().getColumn(5).setCellRenderer(new ColorRenderer());

        //Create the scroll pane and add the table to it.
        JScrollPane scrollPane = new JScrollPane(table);

        //Add the scroll pane to this panel.
        add(scrollPane);
    }

    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("TableDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        TableDemo newContentPane = new TableDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

class ColorRenderer extends DefaultTableCellRenderer {

    public ColorRenderer() {

        setOpaque(true); //MUST do this for background to show up.
    }

    @Override
    public Component getTableCellRendererComponent( JTable table, Object value, boolean isSelected,
            boolean hasFocus,int row, int column) {
        if((int)value == 1) {
            setBackground(Color.BLUE);
        }else {
            setBackground(Color.RED);
        }

        return this;
    }
}

JLabels 和 TextFields 在单独 method/class 中声明时不出现

JLabels and TextFields don't appear when declared in separate method/class

java

swing

jlabel

jpanel

textfield