[Solved] The image’s event handler shows error in Java GUI

Question

Why are you creating new instance of JButton in roll? You just need to change the icon of the buttons which are already displayed on the screen

This…

public void roll() {
    value = nextValue() ;
    if (value==1){
        Icon i=new ImageIcon(getClass().getResource("1.png"));
        c= new JButton(i);
        add(c);
    } else if(value==2){
        Icon im=new ImageIcon(getClass().getResource("2.png"));
        c= new JButton(im);
        add(c);
    }

    repaint() ;
}

should be…

public void roll() {
    value = nextValue() ;
    Icon i = null;
    if (value==1){
        i=new ImageIcon(getClass().getResource("1.png"));
    } else if(value==2){
        i=new ImageIcon(getClass().getResource("2.png"));
    }
    c.setIcon(i);
}

setIcon is a bound field, which means that it will automatically generate a repaint request of it’s own.

If the images are not been updated then it’s likely that your images aren’t been loaded, you can test this in two ways, first, you can set the text of the buttons

public void roll() {
    value = nextValue() ;
    c.setText(Integer.toString(value));
    Icon i = null;
    if (value==1){
        i=new ImageIcon(getClass().getResource("1.png"));
    } else if(value==2){
        i=new ImageIcon(getClass().getResource("2.png"));
    }
    c.setIcon(i);

    repaint() ;
}

and second, you should be using ImageIO.read to load the resources, for example…

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.URL;
import java.util.Random;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;

public class Background extends JFrame {

    private Random ran;
    private int value;
    private JButton r;
    private JButton c;

    public Background() {
        super("title");
        ran = new Random();
        value = nextValue();
        setLayout(new FlowLayout());

        r = new JButton("ROLL ");
        r.setForeground(Color.WHITE);//ndryshon ngjyren e shkrimit
        r.setBackground(Color.YELLOW);
        add(r);

        try {
            BufferedImage die = ImageIO.read(getClass().getResource("1.png"));
            c = new JButton(new ImageIcon(die));
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        add(c);

        thehandler hand = new thehandler(this);//konstruktori i handler merr nje instance te Background
        r.addActionListener(hand);
        c.addActionListener(hand);
    }

    private int nextValue() {
        return Math.abs(ran.nextInt()) % 6 + 1;
    }

    public void roll() {
        value = nextValue();
        c.setText(Integer.toString(value));
        URL path = null;
        if (value == 1) {
            path = getClass().getResource("1.png");
        } else if (value == 2) {
            path = getClass().getResource("2.png");
        }
        try {
            BufferedImage die = ImageIO.read(path);
            c.setIcon(new ImageIcon(die));
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    public int getValue() {
        return value;
    }

    private class thehandler implements ActionListener {

        private Background m;

        thehandler(Background thisone) {
            m = thisone;
        }

        public void actionPerformed(ActionEvent event) {
            m.roll();
        }
    }

    public static void main(String[] args) {
        Background d = new Background();
        d.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        d.getContentPane().setBackground(Color.GREEN);
        d.setSize(700, 500);
        d.setVisible(true);
    }
}

This my throw a NullPointerException, which would mean that Java can’t find your images. Based on your code, you images must be stored within the same package as your class

Have a look at Reading/Loading an Image for more details about ImageIO

The problem with this…

r.roll();//ERROR

is JButton has not roll method

Accepted Answer