How to use the drawing method in JPanel

Question

I am working on a slot machine in Java, and so far I have created a button that will randomly generate two photos. My code compiles, but when I run it, all the material that I put in the drawing method is not displayed. Is there something I can't see? Thanks for your help, and here are some of my codes.

public void paint(Graphics g) { super.paintComponents(g); g.drawString("Int 1 is" + int1,30,30); g.drawString("Int 2 is" + int2,30,80); switch (int1) { case 0: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img, 300, 500, this); break; case 1: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img2,300,500,this); break; case 2: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img3,300,500,this); break; case 3: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img4,300,500,this); break; case 4: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img5,300,500,this); break; case 5: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img6,300,500,this); break; case 6: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img7,300,500,this); break; case 7: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img8,300,500,this); break; case 8: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img9,300,500,this); break; case 9: g.setColor(Color.white); g.fillRect(300,300,300,500); g.drawImage(img10,300,500,this); break; } switch (int2) { case 0: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img, 800, 500, this); break; case 1: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img2,800,500,this); break; case 2: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img3,800,500,this); break; case 3: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img4,800,500,this); break; case 4: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img5,800,500,this); break; case 5: \ g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img6,800,500,this); break; case 6: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img7,800,500,this); break; case 7: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img8,800,500,this); break; case 8: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img9,800,500,this); break; case 9: g.setColor(Color.white); g.fillRect(300,300,800,500); g.drawImage(img10,800,500,this); break; } this.setVisible(true); } 

Answer 1

Problems:

• You draw directly in JFrame - do not do this, as you can ruin JFrame graphics.
• Your overriding of the paint method and calling the super.paintComponents(...) method is again a dangerous thing, and something that should never be done.

Instead, you can draw your drawing in the paintComponent(...) JPanel method and call the correct super.paintComponent(...) method inside it, as described in Downloading drawing lessons , but why bother. It would be much simpler to create an ImageIcons array and just call setIcon(...) on 3 (or how many you need) JLabels after randomly selecting an icon from the array or ArrayList.

Also, never do this:

 try { // .... some code here } catch (IOException e) { } 

At the very least, print a stack trace in the catch block so you can identify any IO exceptions if they occur:

 try { // .... some code here } catch (IOException e) { e.printStackTrace(); // ****** added ******** } 

---

For example, the following code will create this GUI:

 import java.awt.BorderLayout; import java.awt.Color; import java.awt.GridLayout; import java.awt.event.ActionEvent; import java.awt.image.BufferedImage; import java.io.IOException; import java.net.URL; import java.util.ArrayList; import java.util.List; import java.util.Random; import javax.imageio.ImageIO; import javax.swing.*; @SuppressWarnings("serial") // extend JPanel, not JFrame as it gives the class more flexibility as to where to use public class ShowRandomImages extends JPanel { // images from Andrew Thompson example image page, // http://stackoverflow.com/questions/19209650/example-images-for-code-and-mark-up-qas private static final String IMAGE_SHEET_PATH = "http://i.stack.imgur.com/memI0.png"; // how many JLabels to show in a row private static final int LABEL_COUNT = 3; // need to get subimages from image sheet. There are 6 columns in the sheet private static final int IMAGE_COLUMNS = 6; // array of JLabel private JLabel[] labels = new JLabel[LABEL_COUNT]; // hold all the images as ImageIcons read in private List<Icon> imageIconList = new ArrayList<>(); // to randomize the images private Random random = new Random(); // pass the ImageIcon List into this class public ShowRandomImages(List<Icon> iconList) { this.imageIconList = iconList; // jpanel hold row of image-displaying JLabels JPanel labelHolderPanel = new JPanel(new GridLayout(1, 0, 5, 0)); for (int i = 0; i < labels.length; i++) { // create all JLabels in array labels[i] = new JLabel(); labels[i].setBorder(BorderFactory.createLineBorder(Color.DARK_GRAY)); labels[i].setHorizontalAlignment(SwingConstants.CENTER); // center the icon labels[i].setIcon(getRandomIcon()); // initialize with a random image labelHolderPanel.add(labels[i]); // add to holder JPanel } // panel to hold button at bottom JPanel bottomPanel = new JPanel(); // button uses an AbstractAction rather than an ActionListener bottomPanel.add(new JButton(new ShowRandomIconAction("Show Random Image"))); setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5)); setLayout(new BorderLayout()); add(labelHolderPanel, BorderLayout.CENTER); add(bottomPanel, BorderLayout.PAGE_END); } private Icon getRandomIcon() { int randomIndex = random.nextInt(imageIconList.size()); return imageIconList.get(randomIndex); } private class ShowRandomIconAction extends AbstractAction { public ShowRandomIconAction(String name) { super(name); int mnemonic = (int) name.charAt(0); putValue(MNEMONIC_KEY, mnemonic); } @Override public void actionPerformed(ActionEvent e) { for (JLabel jLabel : labels) { jLabel.setIcon(getRandomIcon()); } } } private static void createAndShowGui(List<Icon> imageIconList) { ShowRandomImages mainPanel = new ShowRandomImages(imageIconList); JFrame frame = new JFrame("ShowRandomImages"); frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); frame.getContentPane().add(mainPanel); frame.pack(); frame.setLocationByPlatform(true); frame.setVisible(true); } public static void main(String[] args) { try { final List<Icon> iconList = getImages(); SwingUtilities.invokeLater(new Runnable() { public void run() { createAndShowGui(iconList); } }); } catch (IOException e) { e.printStackTrace(); System.exit(-1); } } // read in image sheet and extract sub-images from it private static List<Icon> getImages() throws IOException { List<Icon> iconList = new ArrayList<>(); URL imageUrl = new URL(IMAGE_SHEET_PATH); BufferedImage imageSheet = ImageIO.read(imageUrl); for (int i = 0; i < IMAGE_COLUMNS; i++) { int x = (int) ((double) i * imageSheet.getWidth() / IMAGE_COLUMNS); int y = 0; int w = imageSheet.getWidth() / IMAGE_COLUMNS; int h = imageSheet.getHeight() / 2; BufferedImage subImage = imageSheet.getSubimage(x, y, w, h); iconList.add(new ImageIcon(subImage)); } return iconList; } } 

Otherwise, if you absolutely must display the images in the drawing method, I would recommend:

• Create a JPanel extension class that displays only one image, for example, ImageDisplayPanel. You will give your class 2 if you need to display 2 images.
• Go to it List<BufferedImage>
• Give it a displayRandomImage() method
• In this method, select a random image from the list and set the BufferedImage field for this image and call repaint ().
• The paintComponent DrawImagePanel method will draw the image held by the field if it is not null.
• In the main GUI, call this method on your 2 or 3 JPanels as needed.