How do I make a rectangle move across the screen with key bindings?

Question

The game I\'m trying to create is snake and so far I\'ve figured out how to use paint(Graphics g) a bit of JPanel, mouse listener and now I\'m tryi

Answer 1

1. You should override paintComponent in your JPanel and call super.paintComponent(g) in it.
2. See How to Use Key Bindings tutorial. Key bindings are preffered in this case rather than a KeyListener
3. pack() then setVisible()
4. You should set global variables for x anf y location, so they can be accessed from within your Action. Then in your actions, increment your x or y and repaint

Try running this example

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

public class KeyBidings extends JFrame {
    int x = 0;
    int y = 0;

    DrawPanel drawPanel = new DrawPanel();

    public KeyBidings(){
        Action rightAction = new AbstractAction(){
            public void actionPerformed(ActionEvent e) {
                x +=10;
                drawPanel.repaint();
            }
        };

            InputMap inputMap = drawPanel.getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW);
            ActionMap actionMap = drawPanel.getActionMap();

        inputMap.put(KeyStroke.getKeyStroke("RIGHT"), "rightAction");
        actionMap.put("rightAction", rightAction);

        add(drawPanel);

        pack();
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
    }

    private class DrawPanel extends JPanel {


        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.GRAY);
                    g.fillRect(0, 0, getWidth(), getHeight());
            g.setColor(Color.GREEN);
            g.fillRect(x, y, 50, 50);
        }

        public Dimension getPreferredSize() {
            return new Dimension(400, 200);
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable(){
            public void run(){
                new KeyBidings();
            }
        });
    }
}

Here's the code you're more concerned with

    Action rightAction = new AbstractAction(){
        public void actionPerformed(ActionEvent e) {
            x +=10;
            drawPanel.repaint();
        }
    };

    InputMap inputMap = drawPanel.getInputMap(JPanel.WHEN_IN_FOCUSED_WINDOW);
    ActionMap actionMap = drawPanel.getActionMap();

    inputMap.put(KeyStroke.getKeyStroke("RIGHT"), "rightAction");
    actionMap.put("rightAction", rightAction);

Create a custom action and add that action to the action map, linked to the input map keystroke. In the action, just increment or, decrement the x and/or y, depending on the direction, then repaint the panel.

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See Key binding tutorial | Graphics tutorial