Troubles with simple animation on image

Question

Im currently trying to make an image (alien.png) to move around the screen randomly and once it hits the walls it comes back. Im actually have so much trouble with this I just can't find a way to upload the image and make it bounce around. this is what I have so far but I'm getting a lot of errors

package animationdemo;


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

import javax.swing.JPanel;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class AnimationDemo extends JFrame {
  public AnimationDemo() {

    Image alien;
    alien = ToolKit.getDefaultToolkit().getImage("alien.png");
        Timer timer = new Timer(50, this);
    timer.start();
  }
  public static void main(String[] args) {
    AnimationDemo frame = new AnimationDemo();
    frame.setTitle("AnimationDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(300, 300);
    frame.setVisible(true);
  }
}

class MovingMessagePanel extends JPanel implements ActionListener {
  public int xCoordinate = 20;
  public int yCoordinate = 20;
  public int xDir=5;  
  public int yDir=5;


  public void actionPerformed(ActionEvent e) {
    repaint();
  }

  @Override
  public void paintComponent(Graphics g) {
    super.paintComponent(g);

    if (xCoordinate > getWidth()) xDir*=-1;
    if (yCoordinate > getHeight()) yDir*=-1;
    if (xCoordinate <0) xDir*=-1;
    if (yCoordinate <0) yDir*=-1;
    xCoordinate += xDir;
    yCoordinate += yDir;
    g.drawImage(alien,xCoordinate,yCoordinate,this);
  }
}

Heres some of the errors I get

AnimationDemo.java:18: error: cannot find symbol
    alien = ToolKit.getDefaultToolkit().getImage("alien.png");
            ^
  symbol:   variable ToolKit
  location: class AnimationDemo
AnimationDemo.java:19: error: incompatible types: AnimationDemo cannot be converted to ActionListener
        Timer timer = new Timer(50, this);
                                    ^
AnimationDemo.java:52: error: cannot find symbol
    g.drawImage(alien,xCoordinate,yCoordinate,this);
                ^
  symbol:   variable alien
  location: class MovingMessagePanel
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
3 errors

I'm just not sure why it can't find the toolkit even thought I imported it also I'm not sure why its not recognizing the alien png on the g.drawImage

Answer 1

Hi
As others said that The errors are self explanatory, i have resolved the errors and modified your code which will be working fine, now the image is moving , the below are modifications
1.Give fully qualified path of image to Toolkit
2.Create MovingMessagePanel object and set alien object
3.Pass MovingMessagePanel object to Timer
4.In your constructor AnimationDemo this.add(messagePannel); so that Panel is visible

import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;

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

public class AnimationDemo extends JFrame  {
    Image alien;
    public AnimationDemo() {


    alien = Toolkit.getDefaultToolkit().getImage("/<Fully Qualified Path>/alien.png");
    MovingMessagePanel messagePannel = new MovingMessagePanel();//Pass this object to Timer
    messagePannel.alien = this.alien;
        Timer timer = new Timer(50, messagePannel);
    timer.start();
    //Add MovingMessagePanel object to JFrame then only it will be visible
    this.add(messagePannel);
  }
  public static void main(String[] args) {
    AnimationDemo frame = new AnimationDemo();
    frame.setTitle("AnimationDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(500, 500);
    frame.setVisible(true);
  }

}

class MovingMessagePanel extends JPanel implements ActionListener {
  public int xCoordinate = 20;
  public int yCoordinate = 20;
  public int xDir=5;  
  public int yDir=5;
  public Image alien;//initialize this with the image

  public void actionPerformed(ActionEvent e) {
    repaint();
  }

  @Override
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    if (xCoordinate > getWidth()) xDir*=-1;
    if (yCoordinate > getHeight()) yDir*=-1;
    if (xCoordinate <0) xDir*=-1;
    if (yCoordinate <0) yDir*=-1;
    xCoordinate += xDir;
    yCoordinate += yDir;
    g.drawImage(alien,xCoordinate,yCoordinate,this);
  }
}

Answer 2

well theres few things which i think might be the problem. first one ToolKit.getDefaultToolkit() you are reffering to different toolkit change that to java.awt.Toolkit.getDefaultToolkit() second one is Timer timer = new Timer(50, this); you cant add your current object which is a jframe as a parameter in the Timer constructor you can implement actionlistner in the AnimationDemo class or you can do it this way

Timer timer = new Timer(50,new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
              //your action
            }
        });
    timer.start(); 

third one is Image alien; its a local variable declared inside your constructor it is not visible to your jpanel. declare Image alien; inside your jframe class(a instance variable)

Image alien;
public AnimationDemo() {
alien = ToolKit.getDefaultToolkit().getImage("alien.png");
  }

Answer 3

The errors are self explanatory:

AnimationDemo.java:18: error: cannot find symbol
    alien = ToolKit.getDefaultToolkit().getImage("alien.png");
            ^
  symbol:   variable ToolKit
  location: class AnimationDemo

You're capitalizing Toolkit wrong. You have to be precise and careful to avoid these errors.

AnimationDemo.java:19: error: incompatible types: AnimationDemo cannot be converted to ActionListener
        Timer timer = new Timer(50, this);
                                    ^

AnimationDemo class does not implement ActionListener, and so you can't use it as such.

AnimationDemo.java:52: error: cannot find symbol
    g.drawImage(alien,xCoordinate,yCoordinate,this);
                ^
  symbol:   variable alien
  location: class MovingMessagePanel

The alien variable is not visible in the program because it is declared in a constructor or method and not in the class.