如何在JFrame中创建JPanel填充整个窗口？

Question

在下面的示例中,如何让JPanel占用所有JFrame？我将首选大小设置为800x420,但它实际上只填充792x391.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.image.BufferStrategy;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class BSTest extends JFrame {
    BufferStrategy bs;
    DrawPanel panel = new DrawPanel();

    public BSTest() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());   // edited line
        setVisible(true);
        setSize(800,420);
        setLocationRelativeTo(null);
        setIgnoreRepaint(true);
        createBufferStrategy(2);
        bs = getBufferStrategy();
        panel.setIgnoreRepaint(true);
        panel.setPreferredSize(new Dimension(800,420));
        add(panel, BorderLayout.CENTER);     // edited line
        panel.drawStuff();
    }

    public class DrawPanel extends JPanel {
        public void drawStuff() {
            while(true) {
                try {
                    Graphics2D g = (Graphics2D)bs.getDrawGraphics();
                    g.setColor(Color.BLACK);
                    System.out.println("W:"+getSize().width+", H:"+getSize().height);
                    g.fillRect(0,0,getSize().width,getSize().height);
                    bs.show();
                    g.dispose();
                    Thread.sleep(20);
                } catch (Exception e) { System.exit(0); }
            }
        }
     }

    public static void main(String[] args) {
        BSTest bst = new BSTest();
    }
}

Answer 1

如果你只有一个框架而没有别的,那么试试这个:

• 在框架中设置BorderLayout.
• 使用BorderLayout.CENTER在框架中添加面板

可能是因为JPanel中的while循环而发生这种情况.(不知道为什么？找到实际原因.找到它时会更新.)如果用paintComponent(g)方法替换它,一切正常:

public BSTest() {
    //--- your code as it is
    add(panel, BorderLayout.CENTER);
    //-- removed panel.drawStuff();
}

public class DrawPanel extends JPanel {
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.BLACK);
        System.out.println("W:" + getSize().width + ", H:" + getSize().height);
        g2d.fillRect(0, 0, getSize().width, getSize().height);
    }
 }

//your code as it is.