Java: Pixel-perfect drawing on JPanel

Question

I'm using OpenJDK 11:

openjdk version "11.0.1" 2018-10-16
OpenJDK Runtime Environment 18.9 (build 11.0.1+13)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.1+13, mixed mode)

Trying to make an app drawing something in JPanel I noticed some annoying inaccuracies.

The following piece of code is supposed to draw a series of lines one below the other (swapping colors are to demonstrate what's happening):

class TestPanel extends JPanel {
@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);

    setBackground(Color.WHITE);

    g.setColor(Color.RED);
    g.drawLine(301, 1, 350, 1);
    g.setColor(Color.BLUE);
    g.drawLine(301, 2, 350, 2);
    g.setColor(Color.GREEN);
    g.drawLine(301, 3, 350, 3);
    g.setColor(Color.RED);
    g.drawLine(301, 4, 350, 4);
    g.setColor(Color.BLUE);
    g.drawLine(301, 5, 350, 5);
    g.setColor(Color.GREEN);
    g.drawLine(301, 6, 350, 6);
    g.setColor(Color.RED);
    g.drawLine(301, 7, 350, 7);
    g.setColor(Color.BLUE);
    g.drawLine(301, 8, 350, 8);
    g.setColor(Color.GREEN);
    g.drawLine(301, 9, 350, 9);
    g.setColor(Color.RED);
    g.drawLine(301, 10, 350, 10);
}

}

However instead of getting lines drawn one below the other there are gaps between some lines:

I suppose this might be caused by something like transformation between a virtual and physical coordinate system.

However how to make it pixel-perfect when preciseness really matters?

Answer 1

I tested it on several jdk releases. Results are: OpenJDK Runtime Environment (build 1.8.0_40-b25): Works correctly
OpenJDK Runtime Environment (build 9+181): Wrong behavior
OpenJDK Runtime Environment 18.3 (build 10.0.2+13): Wrong behavior
OpenJDK Runtime Environment 18.9 (build 11.0.1+13): Wrong behavior

Thank you all for your time and help.