FULL PRODUCT VERSION :
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
macOS Sierra 10.12.2

A DESCRIPTION OF THE PROBLEM :
Javadoc for java.awt.Graphics class declares that outlines of figures are drawn to the right and bottom of 'ideal' outline path. This doesn't happen when rendering happens on a Retina display - outlines seem to be centered on 'ideal' path instead.
The same problem is observed on Windows with latest Java 9 builds, when rendering to a HiDPI display with scale factor 2.
I believe, this is either a bug in the implementation, or in the documentation for java.awt.Graphics class.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the sample program given below on a macOS computer with Retina display.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Black border pixels completely enclose grey inner pixels.
ACTUAL -
At the right and at the bottom of the rectangle black pixels are rendered 'inside' grey pixels.

REPRODUCIBILITY :
This bug can be reproduced always.

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

public class RectangleTest {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            JFrame f = new JFrame();
            f.add(new MyComponent());
            f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            f.setSize(200, 170);
            f.setLocationRelativeTo(null);
            f.setVisible(true);
        });
    }

    private static class MyComponent extends JComponent {
        @Override
        protected void paintComponent(Graphics g) {
            g.setColor(Color.gray);
            g.fillRect(50, 50, 100, 50);
            g.setColor(Color.black);
            g.drawRect(50, 50, 99, 49);
        }
    }
}

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