Resizing icon to fit on JButton in Java?

Solution 1:

There are any number of issues. To start with, all Swing components DON'T auto scale images. Sure, might be a nice idea, but given the amount of time and processing required to do it efficiently, I understand why they don't, so you need to do all the work...

You should also remember, that the size of a component is not determined until it is laid out. And while you can provide all the sizing hints you might like, the layout manager is well within its rights to ignore one or more of these hints.

Instead of "hoping" you know the size of the button, you should make use of the ComponentListener API to receive notifications of when the component is actually resized...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Image;
import java.awt.Insets;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestButton {

    public static void main(String[] args) {
        new TestButton();
    }
    
    private BufferedImage master;
    
    public TestButton() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }
                
                try {
                    master = ImageIO.read(new File("C:\\svg\\Revert 256x256.png"));
                    
                    JButton btn = new JButton() {
                        
                        @Override
                        public Dimension getPreferredSize() {
                            return new Dimension(90, 50);
                        }
                        
                    };
                    btn.addComponentListener(new ComponentAdapter() {
                        
                        @Override
                        public void componentResized(ComponentEvent e) {
                            JButton btn = (JButton) e.getComponent();
                            Dimension size = btn.getSize();
                            Insets insets = btn.getInsets();
                            size.width -= insets.left + insets.right;
                            size.height -= insets.top + insets.bottom;
                            if (size.width > size.height) {
                                size.width = -1;
                            } else {
                                size.height = -1;
                            }
                            Image scaled = master.getScaledInstance(size.width, size.height, java.awt.Image.SCALE_SMOOTH);
                            btn.setIcon(new ImageIcon(scaled));
                        }
                        
                    });
                    
                    JFrame frame = new JFrame("Testing");
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.add(btn);
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (IOException exp) {
                    exp.printStackTrace();
                }
            }
        });
    }
    
}

Note: This example is far from optimised, but simply provides a broad concept of a possible solution...

Now, a word of warning. Image#getScaledInstance is neither the fastest or greatest of scaling algorithms...

Take a look at...

• The Perils of Image.getScaledInstance()
• Quality of Image after resize very low -- Java

for more details...

Solution 2:

You can use the Stretch Icon. Just add the Icon to your component and scaling will happen automatically.