Member Avatar for indienick

Ok, I know this is a stupid-easy question, but how do I "gather" (best word I could think of) an image?

JFrame frame = new JFrame();
Image programIcon = (...?...);
frame.setIconImage(programIcon);

My main issue is that since Image is abstract, I can't exactly go " = new Image("yadda.png");" - like I could with javax.swing.ImageIcon.

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Short practical answer: load a BufferedImage with ImageIO.read(...) (it handles PNG/JPEG reliably and works from inside JARs) and give the JFrame a list of images so the runtime can pick the best size. (docs.oracle.com)

A minimal, reliable pattern (load from classpath and set multiple sizes):

try {
    BufferedImage i16  = ImageIO.read(MyApp.class.getResourceAsStream("/icons/app-16.png"));
    BufferedImage i32  = ImageIO.read(MyApp.class.getResourceAsStream("/icons/app-32.png"));
    BufferedImage i256 = ImageIO.read(MyApp.class.getResourceAsStream("/icons/app-256.png"));
    frame.setIconImages(Arrays.asList(i16, i32, i256));
} catch (IOException e) {
    // fallback: log and/or use a default single image
}

Do the file/network I/O off the Swing Event Dispatch Thread (load images in a background thread or SwingWorker), then update the frame on the EDT. This keeps the UI responsive and avoids subtle threading bugs. (docs.oracle.com)

Notes and pitfalls:

  • ImageIcon is convenient for quick tests because it uses MediaTracker to preload images, but for deterministic loading and better error handling prefer ImageIO.read. Toolkit.getImage(...) / createImage(...) are lower-level and behave differently (caching/async), so they can surprise you unless you handle ImageObserver/MediaTracker. (docs.oracle.com)
  • Provide several sizes (16, 32, 48, 256, etc.) with setIconImages(...) so the OS/JVM can choose the best one. On macOS you may also want the Taskbar API (Taskbar.getTaskbar().setIconImage(...)) for the Dock icon on modern JDKs. (docs.oracle.com)

This complements ’s quick ImageIcon tip and ’ lower-level Toolkit comment: for robust apps use ImageIO + setIconImages + background loading to avoid race conditions and to support multiple display contexts.

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Member Avatar for Rotak

Ok, I know this is a stupid-easy question, but how do I "gather" (best word I could think of) an image?

JFrame frame = new JFrame();
Image programIcon = (...?...);
frame.setIconImage(programIcon);

My main issue is that since Image is abstract, I can't exactly go " = new Image("yadda.png");" - like I could with javax.swing.ImageIcon.

Hi!

Use the derived class ImageIcon.

this.setIconImage(new ImageIcon("...???...")).getImage());

Greetz

Member Avatar for MattEvans

If you do want to ever create an Image, you can use: JPanel.createImage(width, height, null) (it's a member function of quite a few panels, frames, etc). If you want to load an image from a file or webserver use Toolkit.getDefaultToolkit().getImage((url|path)). Images/Graphics can be weird, I've never understood why Image is an abstract class.

Member Avatar for Rotak

I've never understood why Image is an abstract class.

That's pretty simple. You can use a derived class of Image for every kind of image format, even for own formats. So you need to implement some functions, like getGraphics(), on your own...

E.g. you are able to write a class "ZippedImage", which supports reading a single GZipped image file from somewhere. As this class is derived from Image, you can handle it like every other Image object, and it makes no difference to your (e.g.) JFrame, whether you are using ImageIcon or ZippedImage.

Member Avatar for MattEvans

Mm indeed, but it doesn't have to be abstract, I suppose it helps programmers write the extensions (can't compile unless you override abstracts) and even more so in an IDE.

I have an app, and the means I used for creating buffers was to pass a JPanel (or generated Image) right to the "bottom" of the system, either to generate images or work on existing images; not ideal I know. Incidently, what's the actual class of Image that's returned with a call to createImage()?

Matt

Member Avatar for Rotak

Mm indeed, but it doesn't have to be abstract, I suppose it helps programmers write the extensions (can't compile unless you override abstracts) and even more so in an IDE.

I have an app, and the means I used for creating buffers was to pass a JPanel (or generated Image) right to the "bottom" of the system, either to generate images or work on existing images; not ideal I know. Incidently, what's the actual class of Image that's returned with a call to createImage()?

Matt

Well, making Image abstract was one way to do this. Making it an interface would have been the other... but IMHO worse...

Of course, getImage() returns an Image-object, so it doesn't matte what the instance of the object's type is, as long as it's derived from Image.

That's the idea if making it abstract: As long as it's overwriting the abstract methods from Image, it's usable as an image. (Basically that's the idea of any abstract class. :lol: )

Member Avatar for indienick

Thanks alot for your replies :D

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