ADDITIONAL SYSTEM INFORMATION :
Windows 10 Home, version 1809, build 17763.379
openjdk version "12" 2019-03-19
OpenJDK Runtime Environment (build 12+33)
OpenJDK 64-Bit Server VM (build 12+33, mixed mode, sharing)

A DESCRIPTION OF THE PROBLEM :
The setMinimumSize implementation on java.awt.Window and derived classes always treats the specified size as unscaled physical screen pixels, regardless of current DPI scaling.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and run the test program below. When the window appears, attempt to shrink it.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Initial and minimum sizes are identical, therefore it should never be possible to shrink the window.
ACTUAL -
On any DPI setting greater than 100%, the window can be shrunk to the physical equivalent of the specified size. For example, at 200% scale the window size can be halved in both dimensions.

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

public class MinSizeTest extends JFrame {
    private static final long serialVersionUID = 0;

    public static void main(final String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                final JFrame frame = new MinSizeTest();
                frame.setVisible(true);
            }
        });
    }

    MinSizeTest() {
        setTitle("Minimum Size Test");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final Dimension size = new Dimension(400, 400);
        setSize(size);
        setMinimumSize(size);
        setResizable(true);
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
One can listen to the componentResized event and restore a desired minimum size once the window has been resized below that. Unfortunately this produces some annoying flickering. The workaround is described here:
https://news.kynosarges.org/2019/03/14/minimum-size-scaling-for-swing-windows/

FREQUENCY : always