JPanels內部的JLabels居中

Question

我正在製作一個評分計劃，但我遇到了一個問題。我試圖做的是在頂部有一個包含兩個JPanel的JPanel，而JPanel又包含兩個隊名。我很困惑，爲什麼在程序的頂部的兩個JLabel不是他們包含在JPanels內居中。

import java.awt.*; 
import java.awt.event.*; 

import javax.swing.*; 

public class ScoreFrame extends JFrame { 

    private static final Dimension SCREEN_SIZE = Toolkit.getDefaultToolkit().getScreenSize(); 
    private static final int WIDTH = SCREEN_SIZE.width; 
    private static final int HEIGHT = SCREEN_SIZE.height; 
    private final JTextField[] nameField = new JTextField[] { new JTextField(), new JTextField() }; 
    private final JLabel[] nameLabel = new JLabel[] { new JLabel("Team 1"), new JLabel("Team 2") }; 
    private final GridBagLayout gridBag = new GridBagLayout(); 
    private final GridBagConstraints constraints = new GridBagConstraints(); 
    private final JPanel topPanel = new JPanel(); 

    public ScoreFrame() { 
    super(); 
    setResizable(false); 
    setSize(SCREEN_SIZE); 
    setLayout(gridBag); 
    setUndecorated(true); 
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    addKeyListener(new EscapeListener()); 
    addComponents(); 
    } 

    private void addComponents() { 
    addToTopPanel(); 
    constraints.insets = new Insets(0, 0, (int) (HEIGHT * (double) 4/5), 0); 
    gridBag.setConstraints(topPanel, constraints); 

    add(topPanel); 
    } 

    private void addToTopPanel() { 
    final JPanel[] teamPanel = new JPanel[] { new JPanel(), new JPanel() }; 
    topPanel.setLayout(gridBag); 
    topPanel.setSize(new Dimension(WIDTH, HEIGHT/5)); 

    Dimension teamPanelSize = new Dimension(WIDTH/2, HEIGHT/5); 
    teamPanel[0].setSize(teamPanelSize); 
    teamPanel[1].setSize(teamPanelSize); 

    Font nameFont = new Font("Times New Roman", Font.PLAIN, 50); 
    nameLabel[0].setFont(nameFont); 
    nameLabel[1].setFont(nameFont); 

    teamPanel[0].add(nameLabel[0]); 
    teamPanel[1].add(nameLabel[1]); 

    gridBag.setConstraints(teamPanel[0], constraints); 

    constraints.gridx = 1; 
    gridBag.setConstraints(teamPanel[1], constraints); 

    topPanel.add(teamPanel[0]); 
    topPanel.add(teamPanel[1]); 
    } 

    public void paint(Graphics g) { 
    super.paint(g); 
    int strokeSize = ((WIDTH + HEIGHT)/2)/300; 
    if (strokeSize < 1) { 
     strokeSize = 1; 
    } 

    final int fontSize = (int) (strokeSize * 12.5); 

    Graphics2D g2d = (Graphics2D) g; 
    g2d.setStroke(new BasicStroke(strokeSize)); 
    g.drawLine(WIDTH/2, 0, WIDTH/2, HEIGHT/5); 
    g.drawLine(WIDTH/2, (int) (HEIGHT * (double) 105/400), WIDTH/2, HEIGHT); 
    g.drawLine(0, HEIGHT/5, WIDTH, HEIGHT/5); 
    g.drawRect((int) (WIDTH * (double) 45/100), HEIGHT/5, WIDTH/10, (int) (HEIGHT * (double) 3/20)); 

    g2d.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON); 
    g.setFont(new Font("Times New Roman", Font.PLAIN, fontSize)); 
    g.drawString("Errors", (int) (WIDTH * (double) 101/220), HEIGHT/4); 
    } 

    private JFrame getFrame() { 
    return this; 
    } 

    public static void main(final String args[]) { 
    new ScoreFrame().setVisible(true); 
    } 

    public class EscapeListener implements KeyListener { 

    public void keyPressed(final KeyEvent event) { 
     if (event.getKeyCode() == 27) { 
     final int choice = JOptionPane.showConfirmDialog(getFrame(), "Do you want to exit the program?"); 

     if (choice == 0) { 
      System.exit(0); 
     } 
     } 
    } 

    public void keyReleased(final KeyEvent event) { 
    } 

    public void keyTyped(final KeyEvent event) { 
    } 
    } 
} 

Answer 1

調用pack()在使用中的關鍵步驟佈局。此示例使用JLabel.CENTER和GridLayout在框架調整大小時將標籤居中對齊。爲了簡單起見，中心面板只是一個佔位符。這個稍微複雜的example使用了類似的方法以及java.text.MessageFormat。

附錄：但是我怎麼會申請pack()我的代碼？

簡單地調用pack()，如所引用的例子所示。我沒有看到一種簡單的方法來挽救你目前的外部設置尺寸的方法。請改爲getPreferredSize()爲JPanel作爲主要內容。無論屏幕尺寸如何，您的paintComponent()的實施應適應當前尺寸，爲example。

import java.awt.BorderLayout; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.GridLayout; 
import javax.swing.JFrame; 
import javax.swing.JLabel; 
import javax.swing.JPanel; 

/** @see https://stackoverflow.com/a/14422016/230513 */ 
public class Scores { 

    private final JLabel[] nameLabel = new JLabel[]{ 
     new JLabel("Team 1", JLabel.CENTER), 
     new JLabel("Team 2", JLabel.CENTER)}; 

    private void display() { 
     JFrame f = new JFrame("Scores"); 
     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     JPanel teamPanel = new JPanel(new GridLayout(1, 0)); 
     teamPanel.add(nameLabel[0]); 
     teamPanel.add(nameLabel[1]); 
     f.add(teamPanel, BorderLayout.NORTH); 
     f.add(new JPanel() { 

      @Override 
      public Dimension getPreferredSize() { 
       return new Dimension(320, 240); 
      } 
     }, BorderLayout.CENTER); 
     f.pack(); 
     f.setLocationRelativeTo(null); 
     f.setVisible(true); 
    } 

    public static void main(String[] args) { 
     EventQueue.invokeLater(new Runnable() { 

      @Override 
      public void run() { 
       new Scores().display(); 
      } 
     }); 
    } 
}