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

Question

I want to change JButton gradient color, i found this, http://java2everyone.blogspot.com/2009/01/set-jbutton-gradient-color.html, but i want to change gradient for only one button, not all button

Answer 1

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.

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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.