Having trouble displaying graphics in Swing

Question

I've been trying to visually simulate a traffic problem, but for some reason I get only blank output in my swing window. Instead of a constantly-moving picture with vehicles, I get only a grey screen.

My drawing class looks as follows:

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JPanel;

public class RoadNetwork extends JPanel {
     BufferedImage tempicon = ImageIO.read(getClass().getResource("Truck.png"));
     BufferedImage truckicon = new BufferedImage(tempicon.getWidth(), tempicon.getHeight(), BufferedImage.TYPE_INT_ARGB);

     public RoadNetwork() throws IOException {
         repaint();
     }


protected void paintComponent (Graphics g) {
    super.paintComponent(g);
    g.clearRect(0, 0, 600, 600); // insert window size parameters here
    for (int i = 0; i < AMEC.vehiclecounter; i++) {
        if (AMEC.vehicle[i].spawned == true && AMEC.vehicle[i].finished == false) { // if the truck is somewhere on the plant
        g.drawImage(truckicon, AMEC.getcoord(i)[0], AMEC.getcoord(i)[1], this);
        }
    }
    g.drawImage(truckicon, 100, 100, this);
}
}

The call to the class in my main function is done as follows:

RoadNetwork roadnetwork = new RoadNetwork();
roadnetwork.setVisible(true);
JFrame frame = new JFrame();
frame.add(roadnetwork);
frame.setSize(600, 600);
frame.setVisible(true);

Then, with every iteration of my simulation, I call

roadnetwork.repaint();

What am I missing?

Andrew, thanks so much. That was the problem. – Martin Jan 08 '14 at 12:06 — Martin, Jan 08 '14 at 12:06

score 4 · Accepted Answer · answered Jan 08 '14 at 12:08

 BufferedImage tempicon = ImageIO.read(getClass().getResource("Truck.png"));
 BufferedImage truckicon = new BufferedImage(tempicon.getWidth(), tempicon.getHeight(), BufferedImage.TYPE_INT_ARGB);

At the end of the 2nd code line, truckicon is still completely invisible (since it is a transparent image that we have drawn nothing to). Try instead.

 BufferedImage truckicon = ImageIO.read(getClass().getResource("Truck.png"));

score 1 · Answer 2 · answered Jan 08 '14 at 12:22

I hate not knowing why something works. But I remember going through the Graphics totorial and seeing them do this in the constructor where they seem to draw the second image

BufferedImage img = ImageIO.read(imageSrc);
int w = img.getWidth(null);
int h = img.getHeight(null);
BufferedImage bi = new
    BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
Graphics g = bi.getGraphics();
g.drawImage(img, 0, 0, null);

Here's the fix I made. I wish I could give more explanation, but feel free to check out the tutorial I linked

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;

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

public class RoadNetwork extends JPanel {
    BufferedImage tempicon;
    BufferedImage truckicon;

    public RoadNetwork() throws IOException {

        tempicon = ImageIO.read(getClass().getResource("resources/stack_reverse.png"));
        int w = tempicon.getWidth(null);
        int h = tempicon.getHeight(null);
        truckicon = new
            BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);
        Graphics g = truckicon.getGraphics();
        g.drawImage(tempicon, 0, 0, null);
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        //g.clearRect(0, 0, 600, 600); // insert window size parameters here
        // for (int i = 0; i < AMEC.vehiclecounter; i++) {
        // if (AMEC.vehicle[i].spawned == true && AMEC.vehicle[i].finished ==
        // false) { // if the truck is somewhere on the plant
        // g.drawImage(truckicon, AMEC.getcoord(i)[0], AMEC.getcoord(i)[1],
        // this);
        // }
        // }
        g.drawImage(truckicon, 100, 100, this);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable(){
            public void run() {
                try {
                RoadNetwork roadnetwork = new RoadNetwork();
                roadnetwork.setVisible(true);
                JFrame frame = new JFrame();
                frame.add(roadnetwork);
                frame.setSize(600, 600);
                frame.setVisible(true);
                } catch (IOException es) {
                    es.printStackTrace();
                }
            }
        });
    }
}

Also, I was going to suggest @AndrewThompson's answer, but because I didn't know the reason you were using two BufferedImages, I didn't want to suggest it. You may have been trying to do what the tutorial was doing.

Don't forget to call `g.dispose()` on any `Graphics` object your code explicitly creates. — Andrew Thompson, Jan 08 '14 at 12:49
BTW a tip: One way to get image(s) for an example is to hot-link to the images seen in [this answer](http://stackoverflow.com/a/19209651/418556). — Andrew Thompson, Jan 08 '14 at 12:50

Having trouble displaying graphics in Swing

2 Answers2