在Java中将图像加载到背景中

Question

How do you load an image into a background in Java? I have tried many different methods and none of them work so I am asking if anyone knows how to upload a png image into a jpannel

Answer 1

Make your own JPanel. Add an object of PicPanel in your GUI's constructor.

class PicPanel extends JPanel{

    private BufferedImage image;
    private int w,h;
    public PicPanel(String fname){ //Pass picture's filename as a parameter.

        //reads the image
        try {
            image = ImageIO.read(getClass().getResource("/"+fname));
            w = image.getWidth();
            h = image.getHeight();

        } catch (IOException ioe) {
            System.out.println("Could not read in the pic");
            //System.exit(0);
        }

    }

    public Dimension getPreferredSize() {
        return new Dimension(w,h);
    }
    //this will draw the image
    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawImage(image,0,0,this);
    }
}

Answer 2

There are any number of ways this might be achieved.

You Could...

Create a JLabel , apply the image to it's icon property and set this as the frames content pane. You would then need to set the layout manager appropriately, as JLabel doesn't have a default layout manager

JFrame frame = ...;
JLabel background = new JLabel(new ImageIcon(ImageIO.read(...)));
frame.setContentPane(background);
frame.setLayout(...);
frame.add(...);

The problem with this is the JLabel won't resize the image when the frame is resized

You Could...

Create a custom component, extending from something like JPanel and override it's paintComponent method, painting the background as you see fit.

This provides you with the ability to decide how best the image should be scaled when it's available space changes. While there are a number of ways this might be achived, you should read through The Perils of Image.getScaledInstance() to understand the pros and cons of them.

This raises a bunch of new questions, to you want to scale them and preserve the aspect ratio? If so, do you want to fit the image to available area or fill it (so it will always cover the available space)?

Take a look at Java: maintaining aspect ratio of JPanel background image for more details.

Other considerations

Images are generally best loaded through the ImageIO API, as it's capable of loading a wide range of images, but will also throw an IOException when something goes wrong.

See Reading/Loading an Image for more details.

The location of the image is also important. If the image is external to the application (somewhere on the file system), you can use ImageIO.read(new File("/path/to/image")) . However, if the the image is embedded within your application (stored within the Jar for example), you will need to use something more like ImageIO.read(getClass().getResource("/path/to/image")) instead...