Why Doesn\'t My JPanel Update in My Swing Puzzle Game, and How Can I Fix It Using `revalidate()`?

JPanel in Puzzle Game Not Updating

The issue encountered in this puzzle game where the JPanel does not update after adding updated images stems from an incorrect use of addComponents(). While the provided solution suggested overriding paintComponent() to manually redraw the JPanel, a more efficient approach is to use the revalidate() method.

Updated addComponents() Method:

public void addComponents(Img[] im){
    this.removeAll();
    for(int i=0; i<16; i++){
        im[i].addActionListener(this);
        im[i].setPreferredSize(new Dimension(53,53));
        add(im[i]);
    }
    this.revalidate();
}

By calling revalidate(), the JPanel will be notified that its layout has changed and will automatically update its display accordingly. This eliminates the need for manual repainting.

Verified Code:

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

class Puzzle extends JPanel implements ActionListener {
    private int selected_nr=-1;
    private int selected_pl=-1;
    private boolean memory=false;
    private static Img[] images;

    public Puzzle(){
        JFrame f = new JFrame("Smile");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.setSize(252,252);
        f.setVisible(true);

        setLayout(new GridLayout(4, 4));
        images = new Img[16];
        int[] buttons = new int[16];

        for(int i=0; i<16; i++){
            buttons[i] = i;
        }

        int rand;
        int temp;
        Random random;

        random = new Random(System.currentTimeMillis());
        for (int i = 0; i < buttons.length; i++) {
            rand = (random.nextInt() &amp; 0x7FFFFFFF) % buttons.length;
            temp = buttons[i];
            buttons[i] = buttons[rand];
            buttons[rand] = temp;
        }

        for (int i = 0; i < 16; i++) {
            images[i] = new Img(i, buttons[i]);
        }
        addComponents(images);
    }

    public void addComponents(Img[] im){
        this.removeAll();
        for(int i=0; i<16; i++){
            im[i].addActionListener(this);
            im[i].setPreferredSize(new Dimension(53,53));
            add(im[i]);
        }
        this.revalidate();
    }

    public void actionPerformed(ActionEvent e) {
        Img b = (Img)(e.getSource());
        int num = b.getNumber();
        int pl = b.getPlace();

        if(!(b.rightPlace())){
            if(memory){
                if(pl == selected_nr){
                    images[pl].setPlace(selected_pl);
                    images[selected_pl].setPlace(selected_nr);
                    selected_nr = -1;
                    selected_pl = -1;
                    memory = false;
                    addComponents(images);
                }
                else{
                    System.out.println("Try other image");
                }
            }
            else{
                memory = true;
                selected_nr = num;
                selected_pl = pl;
            }
        }
        else{
            System.out.println("OK !");
        }
    }

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

class Img extends JButton {
    int number;
    int place;
    ImageIcon img;

    public Img(int p, int n){
        number = n;
        place = p;
        img = new ImageIcon("u"+number+".jpg", BorderLayout.CENTER);
        setIcon(img);
    }

    public boolean rightPlace(){
        boolean correct=false;
        if(number == place){
            correct = true;
        }
        return correct;
    }
    public void setPlace(int i){
        place = i;
    }
    public int getNumber(){
        return number;
    }
    public int getPlace(){
        return place;
    }
}

With these modifications, the puzzle game should now correctly update the JPanel when new images are added.

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