Java 获取JPanel的大小

我试图从（0,0）到面板中心画一条线。未绘制线，因为DrawingPanel构造函数中的getWidth（）和getHeight（）返回0。我想这是因为框架还不可见。那我怎么才能知道面板的尺寸呢

import java.awt.*;
import javax.swing.*;


public class DrawingApplication extends JFrame {
    static int CenterX;
    static int CenterY;

    public DrawingApplication(){
        setTitle("Drawing Application");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setExtendedState(JFrame.MAXIMIZED_BOTH);
        DrawingPanel pnlDraw = new DrawingPanel();
        add(pnlDraw);
    }

    public static void main(String[] args) {
        DrawingApplication drawingApp = new DrawingApplication();
        drawingApp.setVisible(true);
    }
}


class DrawingPanel extends JPanel {
    int CenterX, CenterY;

    public DrawingPanel(){
        CenterX = getWidth()/2;
        CenterY = getHeight()/2;
    }

    public void paintComponent(Graphics g){
        Graphics2D g2 = (Graphics2D) g;
        super.paintComponent(g);
        g2.drawLine(0, 0, CenterX, CenterY);
    }
}

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有几种方法。最简单的是：

使用

ComponentListener

更新大小，并在触发

ComponentShowed

或

ComponentResistized

时更新大小

只需在每次绘制

JPanel

时获取大小即可