Java getClass().getResource("file") leads to NullPointerException

Question

I am following the Snake Java games tutorial and always get this error:

ImageIcon iid = new ImageIcon(this.getClass().getResource("ball.png"));
ball = iid.getImage();

Exception in thread "main" java.lang.NullPointerException
    at javax.swing.ImageIcon.<init>(Unknown Source)
    at snake2.Board.<init>(Board.java:52)
    at snake2.Snake.<init>(Snake.java:10)
    at snake2.Snake.main(Snake.java:22)

I actually just copied and pasted the code to see how it works. They are in the right packages too; but when I try to run it, I always end up with this error.

Solution 1

The image should be in the same package (folder in OS terms) as the compiled class. Check whether you have both .class and .png in the same folder. If not, you can use classpath-relative paths in getResource(..), by starting with /

Solution 2

Try this:

ImageIcon iid = new ImageIcon(this.getClass()
                  .getClassLoader().getResource("ball.png"));
ball = iid.getImage();

Make sure image is in the same folder as java file.

Solution 3

Try using System.out.println(System.getProperty("java.class.path")); to find out location of your .class file and place the images in this folder.

Solution 4

It is general risky to load resources using relative paths, I'd always recommend using absolute paths, so do

 /ball.png

if the the image is at the root of your classpath, or add a path to the location.

Solution 5

You have to put the image file(ball.png) into your classpath. More details, please take a look at the Javadoc.

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Comments

[kapitanluffy]

so by that you mean i should add the ball.png to the resource?how?

[user207421]

@kapitanluffy: You seem to be using the resources API without knowing the first thing about what it's for. I suggest you read the Javadoc.

[user207421]

Thse two sentences re mutually contradictory. Using the class loader method loses the information about where the .class file is.