Change JButton gradient color, but only for one button, not all

Solution 1:

You can override the paintComponent method of the JButton instance and paint its Graphics object with one of the following classes that implement the Paint interface:

• GradientPaint.
• LinearGradientPaint
• MultipleGradientPaint
• RadialGradientPaint

import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public final class JGradientButtonDemo {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                createAndShowGUI();         
            }
        });
    }

    private static void createAndShowGUI() {
        final JFrame frame = new JFrame("Gradient JButton Demo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(new FlowLayout());
        frame.add(JGradientButton.newInstance());
        frame.setSize(new Dimension(300, 150)); // used for demonstration
        //frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private static class JGradientButton extends JButton {
        private JGradientButton() {
            super("Gradient Button");
            setContentAreaFilled(false);
            setFocusPainted(false); // used for demonstration
        }

        @Override
        protected void paintComponent(Graphics g) {
            final Graphics2D g2 = (Graphics2D) g.create();
            g2.setPaint(new GradientPaint(
                    new Point(0, 0), 
                    Color.WHITE, 
                    new Point(0, getHeight()), 
                    Color.PINK.darker()));
            g2.fillRect(0, 0, getWidth(), getHeight());
            g2.dispose();

            super.paintComponent(g);
        }

        public static JGradientButton newInstance() {
            return new JGradientButton();
        }
    }
}

Solution 2:

A little improvement over mre answer:

private static final class JGradientButton extends JButton{
    private JGradientButton(String text){
        super(text);
        setContentAreaFilled(false);
    }

    @Override
    protected void paintComponent(Graphics g){
        Graphics2D g2 = (Graphics2D)g.create();
        g2.setPaint(new GradientPaint(
                new Point(0, 0), 
                getBackground(), 
                new Point(0, getHeight()/3), 
                Color.WHITE));
        g2.fillRect(0, 0, getWidth(), getHeight()/3);
        g2.setPaint(new GradientPaint(
                new Point(0, getHeight()/3), 
                Color.WHITE, 
                new Point(0, getHeight()), 
                getBackground()));
        g2.fillRect(0, getHeight()/3, getWidth(), getHeight());
        g2.dispose();

        super.paintComponent(g);
    }
}

Solution 3:

TL;DR: it's not possible directly, but can be done with a workaround like in Luca's answer, however his/her answer uses the incorrect gradient steps. The correct ones are listed below.

The way it works

In the Metal LAF there is a hardcoded exception. If the background property is a subclass of UIResource, it's ignored* and the button is instead painted with the (also hardcoded) gradient from the UI property Button.gradient. Otherwise, if background is not a UIResource, that background is painted as-is.

*unless the button is disabled, in which case there is no gradient and the color inside the UIResource is used for the background.

The gradient

Following the logic of MetalButtonUI, I found out the used gradient it uses comes from the UI property Button.gradient, which contains the ArrayList:

0 = {Float} 0.3
1 = {Float} 0.0
2 = {ColorUIResource} "[221,232,243]"
3 = {ColorUIResource} "[255,255,255]"
4 = {ColorUIResource} "[184,207,229]"

Following the logic even further, I ended up in MetalUtils.GradientPainter.drawVerticalGradient(). This implementation interprets the above data as*:

• Gradient from 0% to 30%: color1 to color2
• Gradient from 30% to 60%: color2 to color1
• Gradient from 60% to 100%: color1 to color3

*assuming the second float is 0.0, otherwise more gradients are drawn.

Since this is a multi-stage gradient, it can't be done with a simple GradientPaint but can be done with a LinearGradientPaint. However the background property only accepts Color. It cannot even be spoofed/hacked because the actual value is eventually given to Graphics.setColor() and not Graphics2D.setPaint() (even though Metal is Swing-based and not AWT) Dead End. The only solution seems to subclass JButton altogether.