Java：如何使JPanel中的ImageIcon在随机持续时间内随机出现/重新出现

Question

I am working on an assignment, and I am stuck on one requirement. I have made as much of a good faith effort as I can, and have no choice but to humbly ask for your expertise. My assignment requires that I make a simple game in Java where an image is to appear and reappear randomly for random duration. The user is to click on the image, and if the user clicks on the image, the number of clicks is output to the screen. My main question is how do I make said image appear/reappear at random postitions for random durations? To make the duration random would I somehow set that in the Timer? I tried that and it did not work. As for the random positions, I do not even know how to get started coding that, could someone point me in the right direction? Would I do that in the actionPerformed method?

Anyways, here is my code so far. It compiles, but the movement and speed are smooth and constant. I need the image to appear/reappear randomly instead of "gliding" at a smooth constant rate.

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.swing.*;
import java.util.Random;

public class CreatureClass extends JPanel
{

   private final int WIDTH = 400, HEIGHT = 300;
   private final int DELAY=20, IMAGE_SIZE = 60;

   Random r = new Random();
   private ImageIcon image;
   private Timer timer;
   private int x, y, moveX, moveY;
   private int catchCount=0;

   //-----------------------------------------------------------------
   //  Sets up the panel, including the timer for the animation.
   //-----------------------------------------------------------------
   public CreatureClass()
   {
      timer = new Timer(DELAY, new CreatureListener());//how to make duration random here?

      addMouseListener (new MouseClickedListener());

      image = new ImageIcon ("UMadBro.gif");

      x = 0; //starting coordinates of image
      y = 40;

      moveX = moveY = 3;//image is shifted 3 pixels every time image is updated. I  
                        // tried setting these to a random number, but it makes the 
                        // image "stuck" in one position. 

      setPreferredSize (new Dimension(WIDTH, HEIGHT));
      setBackground (Color.yellow);
      timer.start();
   }

   //-----------------------------------------------------------------
   //  Draws the image in the current location.
   //-----------------------------------------------------------------
   public void paintComponent (Graphics page)
   {
      super.paintComponent (page);
      image.paintIcon (this, page, x, y);
      page.drawString("Number of clicks: " + catchCount, 10, 15);

   }
   //*****************************************************************
   // Detects when mouse clicked=image postition
   //*****************************************************************
   public boolean pointInMe(int posX, int posY)
   {
      if(x == posX && y == posY)
      {
         catchCount++;
         return true;
      }
      return false;
      }
   public int getCatchCount()
   {
      return catchCount;
   }

   private class MouseClickedListener extends MouseAdapter
   {

      public void mouseClicked (MouseEvent event)
      {
         pointInMe(event.getX(), event.getY());

      }
   }

   //*****************************************************************
   //  Represents the action listener for the timer.
   //*****************************************************************
   private class CreatureListener implements ActionListener
   {
      //--------------------------------------------------------------
      //  Updates the position of the image and possibly the direction
      //  of movement whenever the timer fires an action event.
      //  (I don't know how to make the image appear and reappear
      //   randomly for random durations)
      //--------------------------------------------------------------

      public void actionPerformed (ActionEvent event)
      {

         x += moveX;
         y += moveY;

         if (x <= 0 || x >= WIDTH-IMAGE_SIZE)
            moveX = moveX * -1;

         if (y <= 0 || y >= HEIGHT-IMAGE_SIZE)
            moveY = moveY * -1;

        repaint();

      }
    }
 }

Answer 1

Looks like you have defined an instance of java.util.Random named r , and all other needed functionalities have been implemented. So why not just modified the code in actionPerformed with

x = r.nextInt(WIDTH-IMAGE_SIZE);
y = r.nextInt(HEIGHT-IMAGE_SIZE);

This should work for your requirement.

(I'm sorry my reputation is not enough to directly give this simple suggestion by commenting. :(

Answer 2

This is a really good start.

What I would do is create a single use (non-repeating) Swing Timer . This would be started with a random delay (say between 1-5 seconds).

When it ticks, you would determine the current state. If the creature is visible, you would need to stop the main timer (as there's little point in updating it's position while it's invisible), repaint the view and reset the hide/show Timer with a new random value.

If the creature is invisible, you would need to calculate new x/y coordinates and movement direction, restart the main timer and reset the hide/show Timer with a new random value.

In your paintComponent method, you would check a simple visible flag to determine the current state of the creature and determine if you should paint the creature or not.

For example...

(nb: outTimer is javax.swing.Timer , visible is a boolean , rnd is a java.util.Random )

outTimer = new Timer(1000 + (int)(Math.random() * 4000), new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        // Are we currently visible or not
        if (!visible) {
            // Calculate the x/y position
            x = (int) (Math.random() * (WIDTH - IMAGE_SIZE));
            y = (int) (Math.random() * (HEIGHT - IMAGE_SIZE));

            // Calculate a random speed
            int xSpeed = (int) (Math.random() * 4) + 1;
            int ySpeed = (int) (Math.random() * 4) + 1;

            // Calculate the direction based on the speed
            moveX = rnd.nextBoolean() ? xSpeed : -xSpeed;
            moveY = rnd.nextBoolean() ? ySpeed : -ySpeed;
            // Restart the main timer
            timer.start();
        } else {
            // Stop the main timer
            timer.stop();
        }
        // Flip the visible flag
        visible = !visible;
        repaint();
        // Calculate a new random time
        outTimer.setDelay(1000 + (int)(Math.random() * 4000));
        outTimer.start();
    }
});
// We don't want the timer to repeat
outTimer.setRepeats(false);
outTimer.start();

I would also suggest you set the main timer 's initial delay to 0 , timer.setInitialDelay(0); , which will allow to fire immediately the first time it is started

Answer 3

...instead of "gliding" at a smooth constant rate.

CreatureListener is responsible for the animation. Let's replace it with a new ActionListener class, RandomCreatureListener.

timer = new Timer(DELAY, new RandomCreatureListener());

The 'r' field (Random) appears to be unused. It is a clue that you should apply it in RandomCreatureListener. Eg

x = r.nextInt(WIDTH - IMAGE_SIZE);
y = r.nextInt(WIDTH - IMAGE_SIZE);

You'll be getting the desired random pop-ups, but at blinding speeds. You will need to slow it down.

Since this is a assignment, I'll leave it to you to figure it out.