Can paintComponent() be used in an AbstractAction class?

Question

I am trying to make a program that creates a JPanel, and when the user presses W, A, S, and D, a cube that is drawn will navigate around in the window (by a certain amount every time a key is pressed), I have created the MoveCubeUp class, and I override the paintComponent method in it to repaint the cube when it is called, but it will not work. Could someone explain why?

public MyPanel(){
    …
    MoveSquareUp m=new MoveSquareUp(squareX, squareY);
    getInputMap().put(KeyStroke.getKeyStroke(("W"), "pressed"));
getActionMap().put("pressed", m)
}
class MoveSquareUp extends AbstractAction{
    public int squareXX, squareYY;
    public moveSquare(){
    squareXX=squareX+5;
    }
//I define the paintComponent method to draw the rectangle with its set height        
//at squareXX, squareYY
//action method is null (I am still trying to figure out binding keys to    
//actions but the paintComponent not working is preventing that
}

I apologize if that was poorly formatted. 1st post :/ Does the paint method need to be defined within the class that extends JFrame, and if so, how can I use it with an abstractAction class (or how can I avoid the AbstractAction class altogether)?

Answer 1

The crux of your problem is that you need to learn to separate your model from your view from your control. Here the model is the location of your sprite, the view is the GUI that draws this position, and the control will hold the actions including your AbstractAction, and they all should be separate from each other if possible.

So to answer your direct question -- no paintComponent should definitely not be inside of an AbstractAction, since the former is a key part of the view while the latter is a key part of the control. Instead have your view reflect the state of the model, and the model's state will be changed by the control (the actions).

Regarding your other question, should all painting methods be part of the JFrame: none of the painting methods should be in a class extending JFrame since this class is a complex class that creates a top level window and several sub components to display your GUI, and if you override its painting, you can effect painting of sub components in bad ways. Instead draw in the paintComponent method of a class that extends JPanel, and then display this object in your JFrame.

For example:

package pkg3;

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Map;

public class GamePanel extends JPanel {
    private static final int ANIMATION_DELAY = 15;
    private final int HEIGHT = 400;
    private final int WIDTH = 600;
    private Square square;
    private EnumMap<Direction, Boolean> dirMap = new EnumMap<>(Direction.class);
    private Map<Integer, Direction> keyToDir = new HashMap<>();
    // !! private Circle circle;
    private Timer animationTimer;

    public GamePanel() {
        for (Direction dir : Direction.values()) {
            dirMap.put(dir, Boolean.FALSE);
        }
        keyToDir.put(KeyEvent.VK_UP, Direction.UP);
        keyToDir.put(KeyEvent.VK_DOWN, Direction.DOWN);
        keyToDir.put(KeyEvent.VK_LEFT, Direction.LEFT);
        keyToDir.put(KeyEvent.VK_RIGHT, Direction.RIGHT);
        setKeyBindings();
        setBackground(Color.white);
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        setFocusable(true);
        square = new Square();
        animationTimer = new Timer(ANIMATION_DELAY, new AnimationListener());
        animationTimer.start();
    }

    private void setKeyBindings() {
        int condition = WHEN_IN_FOCUSED_WINDOW;
        final InputMap inputMap = getInputMap(condition);
        final ActionMap actionMap = getActionMap();
        boolean[] keyPressed = { true, false };
        for (Integer keyCode : keyToDir.keySet()) {
            Direction dir = keyToDir.get(keyCode);
            for (boolean onKeyPress : keyPressed) {
                boolean onKeyRelease = !onKeyPress; // to make it clear how
                                                    // bindings work
                KeyStroke keyStroke = KeyStroke.getKeyStroke(keyCode, 0, onKeyRelease);
                Object key = keyStroke.toString();
                inputMap.put(keyStroke, key);
                actionMap.put(key, new KeyBindingsAction(dir, onKeyPress));
            }
        }
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        square.display(g);
    }

    private class AnimationListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent evt) {
            boolean repaint = false;
            for (Direction dir : Direction.values()) {
                if (dirMap.get(dir)) {
                    square.move(dir);
                    repaint = true;
                }
            }
            if (repaint) {
                repaint();
            }
        }
    }

    private class KeyBindingsAction extends AbstractAction {
        private Direction dir;
        boolean pressed;

        public KeyBindingsAction(Direction dir, boolean pressed) {
            this.dir = dir;
            this.pressed = pressed;
        }

        @Override
        public void actionPerformed(ActionEvent evt) {
            dirMap.put(dir, pressed);
        }
    }

    private static void createAndShowGUI() {
        GamePanel gamePanel = new GamePanel();
        JFrame frame = new JFrame("GamePanel");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(gamePanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        gamePanel.requestFocusInWindow();
    }

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

enum Direction {
    UP(0, -1), DOWN(0, 1), LEFT(-1, 0), RIGHT(1, 0);
    private int incrX;
    private int incrY;

    private Direction(int incrX, int incrY) {
        this.incrX = incrX;
        this.incrY = incrY;
    }

    public int getIncrX() {
        return incrX;
    }

    public int getIncrY() {
        return incrY;
    }
}

class Square {
    private int x = 0;
    private int y = 0;
    private int w = 20;
    private int h = w;
    private int step = 1;
    private Color color = Color.red;
    private Color fillColor = new Color(255, 150, 150);
    private Stroke stroke = new BasicStroke(3f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);

    public void display(Graphics g) {
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.setColor(fillColor);
        g2d.fillRect(x, y, w, h);
        g2d.setStroke(stroke);
        g2d.setColor(color);
        g2d.drawRect(x, y, w, h);
        g2d.dispose();
    }

    public void setStep(int step) {
        this.step = step;
    }

    public void move(Direction dir) {
        x += step * dir.getIncrX();
        y += step * dir.getIncrY();
    }

}