Java Background Example

ImagePanel.java

package imageBG;

import java.awt.Graphics;
import java.awt.Image;

import javax.swing.JComponent;

public class ImagePanel extends JComponent {
    private Image image;

    public ImagePanel(Image image) {
        this.image = image;
    }

    @Override
    protected void paintComponent(Graphics g) {
        g.drawImage(image, 0, 0, null);
    }
}

Main.java

package imageBG;

import java.awt.image.BufferedImage;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;

import javax.imageio.ImageIO;
import javax.swing.JFrame;

public class Main {
    public Main() {
        try {
            BufferedImage img = ImageIO.read(new URL(
                    "http://static.sixhat.net/nimages/2012/10/bicicleta-na-praca-castelo-em-turim.jpg"));
            JFrame janela = new JFrame("Janela com Background");
            janela.setSize(800, 600);
            janela.setContentPane(new ImagePanel(img));
            janela.setVisible(true);
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        new Main();
    }
}