Re: UIDefaults key?

Knute Johnson <>
Wed, 06 Aug 2014 13:00:35 -0700
On 8/6/2014 11:38, Eric Sosman wrote:

On 8/6/2014 2:17 PM, Knute Johnson wrote:

On 8/6/2014 10:31, Eric Sosman wrote:

On 8/6/2014 12:25 PM, Knute Johnson wrote:

JComponent has a method, getUIClassID(), to return the UIDefaults key
for the ComponentUI subclass. A JTextField returns a key of
TextFieldUI. A typical subclass is

All the interesting details in the UIDefaults however use keys such as
TextField.foreground, TextField.border, TextField.margin etc. Is there
any way to get the prefix, TextField, from the component other than
stripping the UI off the end of the UIClassID?

     Climbing the class hierarchy from MetalTextFieldUI up to
BasicTextFieldUI, I find the method

      * Fetches the name used as a key to lookup properties through the
      * UIManager. This is used as a prefix to all the standard
      * text properties.
      * @return the name ("TextField")
     protected String getPropertyPrefix() {
         return "TextField";

... which sort of looks like what you're after. (But I haven't
researched any other delegate classes, so it's possible they're

I think that is the answer Eric but I just not sure how to get there
from here yet :-).

     Sorry: I somehow thought you already had your hands on an instance
of the ComponentUI subclass -- But now I think you've got nothing but a
JComponent object. Also, I see that the method I stumbled upon is
defined for some ComponentUI subclasses, but not for all.

     Perhaps it's time to take a step back and think about the eventual
goal rather than about one particular (and possibly unworkable) route
toward it. What problem are you trying to solve?

I'm trying to find one of the properties, ???.background, for several
different components. Currently, I get the UIClassID from the component
and lop of the UI at the end and use that as a key to get the value from
UIDefaults. I was hoping to find a way to get the UIDefaults key
directly from the JComponent but I'm not having much luck.

That method you found is the way to go but I don't know how to get
there. I've got the name of the class, I just need to create an
instance and call the getPropertyPrefix() method.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.*;
import javax.swing.plaf.basic.*;

public class test9 {
     public static void main(String... args) {
         EventQueue.invokeLater(new Runnable() {
             public void run() {
                 JTextField tf = new JTextField();
                 String key = tf.getUIClassID();
                 UIDefaults defaults = UIManager.getDefaults();
                 Class<? extends ComponentUI> clazz =


Knute Johnson

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