How to get the painted size of a Swing component?

Question

When I add Swing component (like a JButton) to a JPanel, it renders with it's 'preferred size'.

However, the preferred size is actually larger than the painted button. There appears to be an invisible border around it.

Here's a simple frame with my test panel:

JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

TestPanel pnl = new TestPanel();
frame.getContentPane().add(pnl);

frame.pack();
frame.setVisible(true);

Here's my test panel ...

public class TestPanel extends JPanel {

    JButton btn1 = new JButton("Test1");
    JButton btn2 = new JButton("Test2");

    public TestPanel() {
        this.add(btn1);
        this.add(btn2);
    }

    public void paint(Graphics g) {
        super.paint(g);

        g.setColor(Color.RED);
        Dimension dim = btn1.getPreferredSize();
        g.drawRect(btn1.getX(), btn1.getY(), (int)(dim.getWidth()), (int)(dim.getHeight()));
    }

}

Notice I painted btn1's "PreferredSize" in RED to demonstrate that the preferredSize is actually larger than the button itself.

My question is, how can I determine the width and height of the painted button, not the JButton's preferredSize?

Any help is greatly appreciated, thanks!

UPDATE

Because I actually need this to work for all Swing components, here's a screen shot with the more components.

Unfortunately, I need to figure this out, determining the "real" size of the visible widget is crucial to my application.

Answer 1

I don't think this is particular or practically achievable.

The problem is, the button is using the "unpainted" area to paint other elements, like the focus highlight.

You could try look at the AbstractButton#set/getMargin

Answer 2

If nothing better comes along, note that the authors "recommend that you put the component in a JPanel and set the border on the JPanel."

Addendum: Based on your comments below, it's clear that your question is not about rendering borders but about establishing a component's boundary. What you perceive as unused space is actually reserved by the UI delegate for any number of uses, e.g. selection highlighting or esthetic coherence. You can get an idea of how this varies by selecting different Look & Feel themes in the examples here and here.

Using getbounds():

Using setBorder():

import component.Laf;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;

/**
 * @see https://stackoverflow.com/a/15490187/230513
 */
public class Test {

    private void display() {
        JFrame f = new JFrame("Test");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLayout(new FlowLayout());
        // https://stackoverflow.com/a/11949899/230513
        f.add(Laf.createToolBar(f));
        f.add(decorate(new JButton("Test")));
        f.add(decorate(new JTextField("Test")));
        f.add(decorate(new JTextArea(3, 8)));
        f.add(decorate(new JCheckBox("Test")));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private JPanel decorate(final JComponent c) {
        JPanel p = new JPanel() {
            @Override
            protected void paintComponent(Graphics g) {
                super.paintComponent(g);
                Rectangle r = c.getBounds();
                g.setColor(Color.red);
                // NB pen hangs down and to the right
                g.drawRect(r.x - 1, r.y - 1, r.width + 1, r.height + 1);
            }
        };
        p.add(c);
        return p;
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Test().display();
            }
        });
    }
}