Main thread being interrupted by another thread after run method is called?

Question

I am making a little farm game demo of changing seed to a plant using JLabel, the seed image is initialized after bt1 is clicked, then I used thread to make the label image changed to a grown plant after few seconds time. But I'm having this problem that the seed image is never appearing. Is that because I called run method so the main thread is interrupted by thread time? What should I alter to make the see.jpg show up on JLabel before wheat.jpg taking over it? Here is my code.

public class UI {
    JButton bt1, bt2, bt3, bt4, bt5, bt6;
    JPanel gamePanel;

    public UI(){
        JFrame frame = new JFrame("Little Farm Game");
        JPanel mainPanel = new JPanel(new GridLayout(2,5));
        gamePanel = new JPanel(new GridLayout(3,4));
        JPanel controlPanel = new JPanel(new GridLayout(3,3));
        controlPanel.setBackground(Color.DARK_GRAY);

        bt1 = new JButton("Wheat Seed");
        bt2 = new JButton("Flower Seed");
        bt3 = new JButton("Land Purchase");
        bt4 = new JButton("Wheat Seed Purchase");
        bt5 = new JButton("Flower Seed Purchase");
        bt6 = new JButton("Wallet: "+ Wallet.getInstance().getCurrentMoney());

        Thread time = new Thread(){

            @Override
            public void run() {
                try {       
                    sleep(300);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                for(int i=0; i<gamePanel.getComponentCount(); i++)
                {
                    JLabel label = (JLabel) gamePanel.getComponent(i);
                    label.setIcon(new ImageIcon(getImage("src/wheat.jpg")));
                }
            }
        };

        bt1.addActionListener(new ActionListener(){

        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub

             gamePanel.add(new JLabel(new ImageIcon(getImage("src/flowerseed.jpg"))));
             gamePanel.validate();

               time.run();
            }
        });

        controlPanel.add(bt1);
        controlPanel.add(bt2);
        controlPanel.add(bt3);
        controlPanel.add(bt4);
        controlPanel.add(bt5);
        controlPanel.add(bt6);
        mainPanel.add(gamePanel);
        mainPanel.add(controlPanel);
        frame.add(mainPanel);
        frame.setSize(600, 400);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
    }

    public static Image getImage(final String pathAndFileName) {

        return Toolkit.getDefaultToolkit().getImage(pathAndFileName);
    }
}

Answer 1

1. Don't directly use Threads for this. There's no need, and it carries risk if you call code in a background thread that changes Swing state without care, which is exactly what you're doing .
2. Use a Swing Timer for your animation loop.
3. Display your images as ImageIcons in a JLabel.
4. As mentioned, have the JLabel in your GUI from the get go.
5. Read in your image Icon just once, and save it in a variable or collection.
6. You can easily pause a Swing Timer by simply calling its stop() method, and can restart it just as easily by calling start() .
7. For your benefit and ours, learn and use good Java formatting, especially when posting code on this site. Your current code is all left-justified, making the code difficult to read and understand.

---

For example, and using Andrew's images:

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.ArrayList;
import java.util.List;

import javax.imageio.ImageIO;
import javax.swing.*;

public class ChangingImages extends JPanel {
   public static final String SPRITE_SHEET_PATH = "http://i.stack.imgur.com/SeZ5y.png";
   private static final int DELAY = 400;
   private List<Icon> imageIconList = new ArrayList<>();
   private JLabel label = new JLabel();

   public ChangingImages() throws IOException {
      URL imgUrl = new URL(SPRITE_SHEET_PATH);
      BufferedImage img = ImageIO.read(imgUrl); 
      for (int i = 0; i < 2; i++) {
         for (int j = 0; j < 6; j++) {
            int x = (img.getWidth() * j) / 6;
            int y = (img.getHeight() * i) / 2;
            int w = img.getWidth() / 6;
            int h = img.getHeight() / 2;
            BufferedImage subImg = img.getSubimage(x, y, w, h);
            imageIconList.add(new ImageIcon(subImg));            
         }
      }

      add(label);
      label.setIcon(imageIconList.get(0));

      new Timer(DELAY, new ActionListener() {
         int index = 0;
         @Override
         public void actionPerformed(ActionEvent e) {
            index++;
            index %= imageIconList.size();
            label.setIcon(imageIconList.get(index));
         }
      }).start();
   }

   private static void createAndShowGui() {
      ChangingImages mainPanel = null;
      try {
         mainPanel = new ChangingImages();
      } catch (IOException e) {
         e.printStackTrace();
         System.exit(-1);
      }

      JFrame frame = new JFrame("ChangingImages");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

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