Question

Why does the titlebar overlap the pixels of JPanel. Here some code:

protected void init() {
    this.setContentPane(new MyPanel());
    this.setSize(915, 725);
    this.setVisible(true);
}

class MyPanel extends JPanel {

    @Override
    public void paintComponent(Graphics _g) {
        super.paintComponent(_g);
        Graphics2D g = (Graphics2D)_g;

        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        Font font = new Font("Monospaced", Font.PLAIN, 14);

        g.setFont(font);
        g.setColor(Color.red);

        for(int x=0; x<60; x++) {
            for(int y=0; y< 50; y++) {
                g.drawString("█", x*15, 0);
            }
        }
    }
}

I have added the JPanel to the JFrame and draw some String at y=0.

Answer 1

y = 0 is at the top of the panel, and the coordinates grow downwards. If you want a 20-pixel high line of text to appear just at the top of the panel, then you need to draw it at y = 20. More generally, you can use the FontMetrics class to determine the height of your line of text and use an appropriate offset:

FontMetrics metrics = _g.getFontMetrics(font);
int lineHeight = metrics.getHeight();

In your current code, you’re drawing characters (which are of the order of 20 pixels high) in the cells of a 1-pixel grid. This means that your characters will significantly overlap each other. You’ll want to step your loops by a value much greater than 1 here, to give the characters enough space.