import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class JumpingGame extends JFrame {

    private static final int WIDTH = 400;
    private static final int HEIGHT = 400;
    private static final int GROUND_HEIGHT = 300;

    private int characterY = GROUND_HEIGHT;

    public JumpingGame() {
        setTitle("Jumping Game");
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JumpingPanel jumpingPanel = new JumpingPanel();
        add(jumpingPanel);

        addKeyListener(new JumpingKeyListener());

        Timer timer = new Timer(10, new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                jumpingPanel.update();
            }
        });
        timer.start();
    }

    private class JumpingPanel extends JPanel {

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.BLUE);
            g.fillRect(50, characterY, 30, 30);
        }

        public void update() {
            if (characterY < GROUND_HEIGHT) {
                characterY += 2; // Simulating gravity
                repaint();
            }
        }
    }

    private class JumpingKeyListener implements KeyListener {

        @Override
        public void keyPressed(KeyEvent e) {
            if (e.getKeyCode() == KeyEvent.VK_SPACE && characterY == GROUND_HEIGHT) {
                jump();
            }
        }

        @Override
        public void keyTyped(KeyEvent e) {
            // Not used
        }

        @Override
        public void keyReleased(KeyEvent e) {
            // Not used
        }

        private void jump() {
            // Simulate jumping by moving the character upwards
            characterY -= 50;
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new JumpingGame().setVisible(true);
            }
        });
    }
}
This code creates a simple jumping game where the character jumps when you press the space bar. The JumpingGame class extends JFrame and contains a JumpingPanel class that extends JPanel. The character is represented by a blue rectangle, and jumping is simulated by changing the character's vertical position. The JumpingKeyListener class listens for the space bar key press and triggers the jump.

Note: This is a basic example for educational purposes. In a real game, you would likely use a game engine or a more sophisticated graphics library for better performance and flexibility.