ADDITIONAL SYSTEM INFORMATION :
Windows 11
JDK 21.0.3

A DESCRIPTION OF THE PROBLEM :
LineBorder does not scale correctly. With my OS set to 150% scale for example, the width of the LineBorder is the same as with my OS at 100% scale.

The bug is new since JDK 17.0.3. It works as expected in that version.

I believe the bug is in the following line of code in javax.swing.border.LineBorder:

  int offs = this.thickness * (int) scaleFactor;

Note how scaleFactor is cast to an int before being used, thus losing the fractional part! This means that a scaling factor of 1.5 will result in an effective scale factor of 1. And a scale factor of 0.5 will result in an effective scale factor of 0 (making the border disappear entirely).

REGRESSION : Last worked in version 17

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Set your OS scaling to 150% via the OS settings
2. Run the code below
3. Print screen the Java app and paste it to a paint program
4. Measure the width of the red border in pixels

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The border is 15 pixels wide
ACTUAL -
The border is 10 pixels wide

---------- BEGIN SOURCE ----------
import javax.swing.*;
import javax.swing.border.LineBorder;
import java.awt.*;

public class LineBorderBug {
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(100, 100);
        JPanel panel = new JPanel();
        panel.setBorder(new LineBorder(Color.RED, 10));
        frame.add(panel);
        frame.setVisible(true);
    }
}
---------- END SOURCE ----------

FREQUENCY : always