Develop Reference

NullPointerException while getting an Image

I am having trouble setting images in my newest game. When I call the method getImage(String), and I get the Image like so:
Image head = getImage("Torso_model_01.png");
I get the following error message:
Err: java.lang.NullPointerException
At PB2Main.Body(Body.java : 27)
...
and so on...
On this tutorial, it explains how to get an image using ImageIcon like so:
String imgFile = "Images/" + img;
URL imgURL = getClass().getClassLoader().getResource(imgFile);
ImageIcon imageIcon;
Image image;
if(imgURL != null){
imageIcon = new imageIcon(imgURL);
image = imageIcon.getImage();
}
final Image anImage = image;
I made a method for this:
public URL getURL(String img){
String imgFile = "Images/" + img;
URL imgURL = getClass().getClassLoader().getResource(imgFile);
return imgURL;
}
Then I made a method called getImage(String)
public Image getImage(String img) {
ImageIcon imageIcon;
Image image;
URL imgURL = getClass().getClassLoader().getResource(getURL(img));
if(imgURL != null){
imageIcon = new ImageIcon(imgURL);
image = imageIcon.getImage();
return image;
}
System.err.println("Unable to Locate Image: " + imgURL);
}
Now, I have a class called Body.
In that class, I have a constructor:
public Body(float x, float y, String head, String torso){//atm this is just so i can get the image to actually draw on the screen
Image Head = debugger.getImage(head);// debugger doubles as a library and debugger
//i also can't have this class extend debugger otherwise it will create a window :/
// is that a glitch or something in Java? :L perhaps i just don't understand
// inheritance very well and what happens exactly when you inherit a class :(
Image Torso = debugger.getImage(torso);
g2.drawImage(Head, canvas.geWidth()/ 2,canvas.getHeight()/2, null)// canvas: the window to
//draw to
// can someone also quickly explain in their answer what an image observer is please?
g2.drawImage(Torso, Head.getX() - 5, Head.getY() - 5, null);
}
The compiler gives me the following error message:
java.lang.NullPointerException
At PlazmaBurst2.Body(Body.java: 37)
//the code it brings me to is line 1 in the constructor:
/* null: */ Image Head = debugger.getImage(img);
I don't understand where this NullPointerException is coming from. I did it exactly how they do it in the Custom Graphics Programming section of the same site.
The code works fine if I just copy and paste the code, but not if I use the method getImage(String).

You're problem is on line 3 of getImage(String):
URL imgURL = getClass().getClassLoader().getResource(getURL(img));
This should be changed to:
URL imgURL = getURL(img);

Java Applet Image Load

I want to display an image icon in my applet.I created a package resources and saved my image in it.This is what i tried :-
Image logo;//I declare globally
logo = getImage("logo.jpg");//I initialize in the constructor
And i use this proceedure
public Image getImage(String name){
URL imgUrl = getClass().getClassLoader().getResource("resources/"+name);
ImageIcon icon = new ImageIcon(imgUrl);
return icon.getImage();
}
public void paint(Graphics g)
{
if (logo!=null){
g.drawImage(logo, 30, 30, null);
}
g.drawString("Hwllo", 12, 12);
}
Then i call the:
repaint() //In the Constructor
But i dont see an image or my String.What might be the problem.Moreover is there any easier method to load images in the Applet??

You setting the URL to the
URL imgUrl = getClass().getClassLoader().getResource("resources/"+name);
ImageIcon icon = new ImageIcon(imgUrl);
But while Calling paint method, you are calling the logo variable
g.drawImage(logo, 30, 30, this);
The problem is in your setting URL value, set URL to your logo variable like
URL url = new URL(/*Your resources herre*/, /*Your file name here*/);
logo=getImage(url);
After that display image using paint method.

Error loading image to set background

I am trying to load an image and set to background, but i get the error at selectionPanel method "Could not load background image".
It seems that something is going wrong with the image processing but i cant find out what.
public class selectionPanel extends JPanel
{
//Variable with the name of our pic
private static final String path = "selbkgrnd.jpg";
private ImageIcon imageIcon;
private Dimension windowSize;
private int imageHeight;
private int imageWidth;
protected selectionPanel()
{
this.imageIcon = new ImageIcon("selbkgrnd.jpg"); //Save image to imageIcon
Image image = this.imageIcon.getImage();
this.imageWidth = image.getWidth(null);
this.imageHeight = image.getHeight(null);
if ((this.imageWidth == -1) || (this.imageHeight == -1)) //Check if background image is succesfully loaded
{
JOptionPane.showMessageDialog(JOptionPane.getDesktopPaneForComponent(this), "Could not load background image", "Fatal error!", 0);
System.exit(-1);
}
this.windowSize = new Dimension(this.imageWidth, this.imageHeight);
}
protected void startScreen()
{
setOpaque(false);
setSize(this.windowSize);
}
protected int getImageHeight()
{
return imageHeight;
}
protected int getImageWidth()
{
return imageWidth;
}
#Override
public void paintComponent(Graphics g)
{
g.drawImage(this.imageIcon.getImage(), 0, 0, null);
super.paintComponent(g);
}
}

Usually this is due to your looking in the wrong location for your Image File. Try using the complete path to the image, either that or a path relative to the user's directory which can be found with:
System.out.println("user directory: " + System.getProperty("user.dir"));
Edit
You state:
Thank you it worked with the full path, but isnt it supposed to work with just the image name if it is inside the source code folder ?
No. Again, Java will look for the file relative to the user directory.
Note however that if the image is in the class file directory or in a directory relative to this and you make a jar file out of this and need to access the images, then you can't use files. You will need to get the images as a resource and the relative path will be different since it won't be related to the user.dir but rather will be relative to the location of the class files.

Can't define a path to an image

I imported an image into Eclipse, in the same package as this class:
public class mainWindow extends JFrame {
public mainWindow() {
Image bg = // \mainPackage\ShittyPlane.png;
Graphics2D g2d;
this.setSize(500,500);
this.setResizable(false);
this.setTitle("GameTest");
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
this.setVisible(true);
g2d.drawImage(bg, 0, 0, null);
}
}
How do I define the image path?

If the image is part of you source and is packed into jar later for distribution i would sucgest you get a stream to the image using getResourceAsStream.
ClassLoader cl = getClass().getClassLoader();
InputStream is = cl.getResourceAsStream("mainPackage/ShittyPlane.png");
BufferedImage image = ImageIO.read(is);
this aproache will also work in if you run the program from your IDE
If you plan to locate the image using a a File chooser then go with #Pescis's answer.

What you need to do to load an image from a specific file is:
BufferedImage img = null;
try {
img = ImageIO.read(new File("src/mainPackage/ShittyPlane.png")); //I'm guessing this is the path to your image..
} catch (IOException e) {
}
For more info you can read the javadoc on working with images.

Will setShape() clear the background of a JFrame?

I would like to write a program in java...
I want to set the shape of the window(a JFrame) to a set of PNG Images(with a transparent background).
(Actually, I would like to make the window change its shape continual, and it look like an animation!)
And, I read images from files,save them to a array, then, I use class GeneralPath to get the area of my animated character(in png images), save it to areaArray.
After all things are done, I start the paint thread. It works well...But sometimes the window would flash(ah...I mean a flicker happened, but the background color I saw when flashing is transparent, I could saw my desktop wallpaper!).
I don't want to see the flicker/flash again, would someone help me? Thanks!
P.S. : Sorry for my poor English!
public class JCustomFrame extends JFrame implements Runnable
{
private final int max_frame=18; //Here is the max numbers of my png images
private BufferedImage[] BufImageArray; //The array to save all the png images
private BufferedImage nowImage; //Save the image to be drawn in this turn
private int counter; //Indicate which png image to be drawn
private Area[] areaArray; //Save the shapes of the animated character in each png image
public void run()// a thread function to paint the frame continual
{
while(true){
if(counter==max_frame)counter=0;
nowImage=BufImageArray[counter];
setShape(areaArray[counter]);
repaint();
try{
Thread.sleep(100);
}catch(InterruptedException e){
System.out.println("Thread.sleep error!");
}
counter++;
}
}
public JCustomFrame()
{
super();
setUndecorated(true);
setBackground(new Color(0,0,0,0));
counter= 0;
//...some codes here
new Thread(this).start();
}
public void paint(Graphics graphic)
{
graphic.drawImage(nowImage,0,0,this);
}
}
Here is a sample code to run the program:
import javax.swing.*;
public class MainFrame
{
public static void main(String[] args)
{
JCustomFrame myFrame = new JCustomFrame();
myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myFrame.setSize(300,400);
myFrame.setVisible(true);
return ;
}
}
I modified 2 lines above, the "png file name" and the "max_frame" to apply the new image files.
I found that if I put the same program on Windows rather than my OpenSuse, it works very well(without the flicker), here I upload all the pack of my source(include the image file).
Here my code is.
Thanks again.
==================================================================================
Thanks Andrew Thompson for suggestions.
This time, I try to delete the codes unrelated to the problem, and paste a gif to show the situation. The codes above isn't runnable, but the source code in the link works well.
P.S. The flicker/flash happened in random frame, isn't completely the same as the gif shows.
('cause I could only add a transparent panel in my gif image at a fixed sequence)
Thanks!!