Java在JPanel上看不到图形

Question

I am using Java Eclipse with Swing Designer and I am trying to display some graphics on a JPanel. I am a pretty amateurish programmer and new to graphics coding.

Basically, There is a JFrame with 2 JPanels( Stage and Setttings). There is a method paintTest inside the class Surface. This method should draw the string 'This is a test' on the Stage JPanel. When I execute the code there are no errors. Any help would be appreciated.

Please see the below code.

import java.awt.Color;
import java.awt.Component;
import java.awt.EventQueue;

import javax.swing.JFrame; 
import javax.swing.JPanel;
import javax.swing.border.BevelBorder;
import javax.swing.JLabel;
import java.awt.Font;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Window;



public class TestSimulator extends JFrame{

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private JFrame frmTestSimulation;
    private JPanel stagePanel = new JPanel();
    private JLabel stageLabel = new JLabel("Stage");
    private JPanel settingsPanel = new JPanel();
    private JLabel settingsLabel = new JLabel("Settings");


    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    TestSimulator window = new TestSimulator();
                    window.frmTestSimulation.setVisible(true);

                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public TestSimulator() {
        initialize();
    }


    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frmTestSimulation = new JFrame();
        frmTestSimulation.setTitle("WAPP Simulation");
        frmTestSimulation.setBounds(100, 100, 727, 500);
        frmTestSimulation.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frmTestSimulation.getContentPane().setLayout(null);

        //JPanel stagePanel = new JPanel();
        stagePanel.setBorder(new BevelBorder(BevelBorder.RAISED, null, null, null, null));
        stagePanel.setBounds(262, 11, 439, 439);
        frmTestSimulation.getContentPane().add(stagePanel);
        stagePanel.setLayout(null);
        stagePanel.add(new Surface());  //Show the string 'This is a test'

        //JLabel stageLabel = new JLabel("Stage");
        stageLabel.setFont(new Font("Tahoma", Font.BOLD, 14));
        stageLabel.setBounds(183, 11, 53, 34);
        stagePanel.add(stageLabel);

        //JPanel settingsPanel = new JPanel();
        settingsPanel.setBorder(new BevelBorder(BevelBorder.RAISED, null, null, null, null));
        settingsPanel.setBounds(10, 11, 242, 439);

        frmTestSimulation.getContentPane().add(settingsPanel);
        settingsPanel.setLayout(null);

        //JLabel settingsLabel = new JLabel("Settings");
        settingsLabel.setFont(new Font("Tahoma", Font.BOLD, 14));
        settingsLabel.setBounds(78, 11, 71, 22);
        settingsPanel.add(settingsLabel);

    }

    class Surface extends JPanel{

        public void paintTest(Graphics g)
        {
            Graphics2D g2d = (Graphics2D) g;
            g2d.drawString("This is a test", 50, 50);

        }

        @Override
        public void paintComponent(Graphics g) {

            super.paintComponent(g);
            paintTest(g);
        }



    }
}

Answer 1

Your stagePanel is lacking a layout, so only one component inside of it will be printed. Change

stagePanel.setLayout(null);

to

stagePanel.setLayout(new GridLayout(1, 2));

And it should display something like

Refer to this website for more information about layouts in Swing and to this answer to learn more about displaying custom stuff in JPanels.