Why are my JPanels not showing color or shapes

问题

So whenever I run the application the frame is there however all the colors and rectangles are not. I'm making 3 different menus each intractable so I need 3 panels within my frame

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

public class Application extends JPanel{

    public static void main(String[] args) {

        JFrame frame = new JFrame("FrogVibes");
        JPanel container = new JPanel();
        JPanel mainPanel = new JPanel();
        JPanel upgradePanel = new JPanel();
        JPanel frogPanel = new JPanel();
        JButton button = new JButton();

        mainPanel.setSize(400,690);
        upgradePanel.setSize(400,690);
        frogPanel.setSize(400,690);
        mainPanel.setBackground(Color.BLACK);
        upgradePanel.setBackground(Color.BLACK);
        frogPanel.setBackground(Color.BLACK);

        container.setLayout(new BoxLayout(container, BoxLayout.X_AXIS));
        container.add(mainPanel);
        container.add(upgradePanel);
        container.add(frogPanel);

        new Application() {
        };

        frame.setContentPane(new Container());
        frame.setSize(1280,700);
        frame.setVisible(true);
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

    }

    public void Graphics(Graphics g) {
        super.paintComponent(g);
        g.drawRect(0,700,400,100);
        g.drawRect(0, 600,100,150);
    }
}

what is wrong placement, a missing statement, or what

回答1:

You need to create an instance of your Application class and add it to a JFrame:

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

public class Application extends JPanel{

    public static void main(String[] args) {

        JFrame frame = new JFrame("FrogVibes");
        JPanel application = new Application();
        frame.add(application);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawRect(0,700,400,100);
        g.drawRect(0, 600,100,150);
    }
}

Also, the method must be named paintComponent(), not Graphics(). Now Swing will call paintComponent() when it draws the window.

回答2:

You have just a miss typos, you need to add container that you created to the frame like so frame.setContentPane(container); instead of adding a new container. and I just change colors so that you can see each panel :

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

public class Application extends JPanel{

    public static void main(String[] args) {

        JFrame frame = new JFrame("FrogVibes");
        JPanel container = new JPanel();
        JPanel mainPanel = new JPanel();
        JPanel upgradePanel = new JPanel();
        JPanel frogPanel = new JPanel();
        JButton button = new JButton("button!");

        mainPanel.setSize(400,200);
        upgradePanel.setSize(500,690);
        frogPanel.setSize(400,690);
        mainPanel.setBackground(Color.RED);
        upgradePanel.setBackground(Color.BLACK);
        frogPanel.setBackground(Color.BLUE);
        
        upgradePanel.add(button);

        container.setLayout(new BoxLayout(container, BoxLayout.X_AXIS));
        container.add(mainPanel);
        container.add(upgradePanel);
        container.add(frogPanel);

        new Application() {
        };

        frame.setContentPane(container);
        frame.setSize(1280,700);
        frame.setVisible(true);
        
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

}

public void Graphics(Graphics g) {
    super.paintComponent(g);
    g.drawRect(0,700,400,100);
    g.drawRect(0, 600,100,150);
}
}

来源：https://stackoverflow.com/questions/62764439/why-are-my-jpanels-not-showing-color-or-shapes

标签

java

swing

jpanel