如何将图形放在JPanel上？

我在向JPanel添加图形时遇到问题。 如果我从panel.add更改行（new graphics（））; to frame.add（new graphics（））; 并且不要将JPanel添加到JFrame，JFrame上会出现黑色矩形。 我只是不能让黑色矩形出现在JPannel上，并想知道是否有人可以帮助我。

import java.awt.*; import java.awt.event.*; import javax.swing.*; public class Catch{ public class graphics extends JComponent{ public void paintComponent(Graphics g){ super.paintComponents(g); g.fillRect(200, 62, 30, 10); } } public void createGUI(){ final JFrame frame = new JFrame(); JPanel panel = new JPanel(); frame.setSize(500,500); frame.addMouseListener(new MouseAdapter(){ public void mouseClicked(MouseEvent e) { System.out.println(e.getPoint().getX()); System.out.println(e.getPoint().getY()); } }); panel.add(new graphics()); frame.add(panel); frame.setVisible(true); frame.setDefaultCloseOperation(frame.DISPOSE_ON_CLOSE); } public static void main(String[] args){ Catch GUI= new Catch(); GUI.createGUI(); } } 

Answer 1

自定义组件为0x0 px。

 import java.awt.*; import javax.swing.*; public class Catch { public class MyGraphics extends JComponent { private static final long serialVersionUID = 1L; MyGraphics() { setPreferredSize(new Dimension(500, 100)); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); g.fillRect(200, 62, 30, 10); } } public void createGUI() { final JFrame frame = new JFrame(); JPanel panel = new JPanel(); panel.add(new MyGraphics()); frame.add(panel); frame.pack(); frame.setVisible(true); frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); } public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { @Override public void run() { Catch GUI = new Catch(); GUI.createGUI(); } }); } } 

Answer 2

这是你可以看到的东西：

 import javax.swing.*; import java.awt.*; public class GraphicsOnJPanel extends JFrame { public GraphicsOnJPanel () { setSize (Toolkit.getDefaultToolkit ().getScreenSize ()); setResizable (false); setContentPane (new JPanel () { public void paint (Graphics g) { g.setColor (Color.RED); g.fillRect (100, 100, 100, 100); } } ); setVisible (true); } public static void main (String args[]) { new GraphicsOnJPanel (); } } 

也许这有用吗？