为什么我的图标处理代码会抛出 NullPointerException？

Question

I have added an image for my button,but when I run that frame this exception will be thrown.why?please help me.

init:

deps-jar:
compile-single:
run-single:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javax.swing.ImageIcon.<init>(ImageIcon.java:138)
        at ClientGUI.IdAndPasswordFrame.initComponents(IdAndPasswordFrame.java:91)
        at ClientGUI.IdAndPasswordFrame.<init>(IdAndPasswordFrame.java:22)
        at ClientGUI.IdAndPasswordFrame$4.run(IdAndPasswordFrame.java:200)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
BUILD SUCCESSFUL (total time: 1 second)

line 138:

public ImageIcon (URL location) {
    this(location, location.toExternalForm());
}

line91:

 jButton1.setIcon(new javax.swing.ImageIcon(getClass().getResource("/Images/yahoo_1.gif"))); // NOI18N

I use this poor checking (Peter Lang recommended)which is:System.out.println(getClass().getResource("/Images/yahoo_1.gif")); and it returns null,why? please help me.

Answer 1

This means, that getClass().getResource("/Images/yahoo_1.gif") returns null .

JavaDoc states that this happens if

the resource could not be found or the invoker doesn't have adequate privileges to get the resource.

1. Check if getResource really returns null :
   System.out.println(getClass().getResource("/Images/yahoo_1.gif"));

2. Make sure that your path is correct and that it is in your classpath.

EDIT :

I just tried it with NetBeans. I created the following structure

Source Packages
  Images
    yahoo_1.gif

and your code worked fine. Is this your structure?

Try to right-click on your application and select Clean and Build .

Answer 2

In order to fix this, the images need to be copied in the bin directory - not in src directory.

Otherwise you will get null all the time on getClass().getResource("image.png") . The path is not null and you can set it as the above - only if you copy the images that you need inside the binary directory, where .class files for your project are located.

This fixed the problem. Let me know if I helped in this.

Ioana

Answer 3

It looks like getClass().getResource("/Images/yahoo_1.gif") returns null ie the .gif cannot be found on your classpath. (Images versus images maybe?)

Answer 4

The URL being passed in is null from this line:

getClass().getResource("/Images/yahoo_1.gif")

From the JDK documentation:

[getResource(..) returns] A URL object for reading the resource, or null if the resource could not be found or the invoker doesn't have adequate privileges to get the resource

Maybe you meant ("Images/yahoo_1.gif") - ie relative path not absolute?

Answer 5

I had the same problem. What worked for me was:

1. Look into the jar file or in the bin folder(the one with .class files) and see the path of image.
2. List item

Answer 6

private class HandlerClass implements ActionListener{
        public void actionperformed(ActionEvent event){
            JOptionPane.showMessageDialog(null, String.format("%s", event.getActionCommand()));
        }

}

Answer 7

After reviewing some things when trying to add an image I was presented with the same problem that usually occurs in project with maven.

I found a solution that uses the full path to be able to access the image. Also, create a function that returns an icon with the image and automatically scaled according to the dimensions that are sent to it.

Path -> directory where the image is located, width -> width of the icon, heigth-> height of the icon I hope it serves you, this is my first contribution in the community

public Icon getIcon(String ruta, int width, int heigth) {
        Image image = (new ImageIcon(ruta)).getImage().getScaledInstance(width, heigth, 0);
        Icon mIcono = new javax.swing.ImageIcon(image);
        return mIcono;
    }