Class.getResource () returns null

Question

I try to display images on a JPanel, but I keep getting an error:

java.lang.IllegalArgumentException: input == null!

I do not understand what's going on.

Here is the code I'm using:

public void actionPerformed(ActionEvent e) { try { Image image=ImageIO.read(getClass().getResource("img/" +num.getText()+".jpg")); Image resized = image.getScaledInstance(200, 200, 100); pictureFrame.setIcon(new ImageIcon(resized)); } catch (Exception ex){ ex.printStackTrace(); } } 

It just makes me get an error!

The stack trace creates the following:

 Java.lang.IllegalArgumentException: input == null! at javax.imageio.ImageIO.read(ImageIO.java:1362) at work.Item.actionPerformed(Item.java:96) at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995) at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318) at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387) at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236) at java.awt.Component.processMouseEvent(Component.java:6297) at javax.swing.JComponent.processMouseEvent(JComponent.java:3275) at java.awt.Component.processEvent(Component.java:6062) at java.awt.Container.processEvent(Container.java:2039) at java.awt.Component.dispatchEventImpl(Component.java:4660) at java.awt.Container.dispatchEventImpl(Container.java:2097) at java.awt.Component.dispatchEvent(Component.java:4488) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4575) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4236) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4166) at java.awt.Container.dispatchEventImpl(Container.java:2083) at java.awt.Window.dispatchEventImpl(Window.java:2489) at java.awt.Component.dispatchEvent(Component.java:4488) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:668) at java.awt.EventQueue.access$400(EventQueue.java:81) at java.awt.EventQueue$2.run(EventQueue.java:627) at java.awt.EventQueue$2.run(EventQueue.java:625) at java.security.AccessController.doPrivileged(Native Method) at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87) at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98) at java.awt.EventQueue$3.run(EventQueue.java:641) at java.awt.EventQueue$3.run(EventQueue.java:639) at java.security.AccessController.doPrivileged(Native Method) at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87) at java.awt.EventQueue.dispatchEvent(EventQueue.java:638) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122) 

How can i solve this? I checked the location of the image and tried from different places and always got the same error!

I am using NetBeans environment.

Answer 1

Assuming getClass() returns com.foo.bar.MyActionListener , getClass().getResource("img/foo.jpg") looks for a file named foo.jpg in the package com.foo.bar.img . If the image is not in this package or it is in this package, but its root directory is not in the class path, the method returns null.

If the img folder is at the root of the class path, you should use getClass().getResource("/img/foo.jpg") (note the start of / ) or getClass().getClassLoader().getResource("img/foo.jpg") .

Answer 2

You must specify the relative path for the source file. For example, if you have this:

 src --img --classes 

And you are in the classes folder, you should write this:

 getClass().getResource("../img/" +num.getText()+".jpg")