在椭圆上画线

Question

I must write a text on an oval or circle I have this code(I found it on Stackoverflow) but I don't understand some points.

import java.awt.Color;
import java.awt.FontMetrics;
import java.awt.Graphics;
import javax.swing.JPanel;

public class Panneau extends JPanel {
    @Override
    public void paintComponent(Graphics g){
        // Declaration 
        String text = "test";
        int x = 100, y = 50;
        int ovalWidth = 50, ovalHeight = 50;

        // Draw circle
        g.setColor(Color.blue);
        g.fillOval(x-ovalWidth/2, y-ovalHeight/2,ovalWidth, ovalHeight);
        // I don't understand why x-ovalwidth/2 and y-ovalheight/2

        // Put text into circle
        FontMetrics fm = g.getFontMetrics();
        double textWidth = fm.getStringBounds(text, g).getWidth();
        // What is the job of getstringbounds 
        g.setColor(Color.white);
        g.drawString(text, (int) (x - textWidth/2),(int) (y + fm.getMaxAscent() / 2));
    } 
}

and thanks

Answer 1

Using information from the Graphics Documentation

fillOval( x, y, width, height)

x - the x coordinate of the upper left corner of the oval to be filled.
y - the y coordinate of the upper left corner of the oval to be filled.
width - the width of the oval to be filled.
height - the height of the oval to be filled.

So you are telling the graphics to draw a circle where the top-left is at x - (half the width), y - (half the height). Reason being, it offsets the circle so the center of the circle is at (x, y) instead of the top-left.

getStringBounds

Returns:
a Rectangle2D that is the bounding box of the specified String in the
specified Graphics context.

(Returns a rectangle that is big enough for the String)

Needless to say, the documentation is very helpful to look at when you are using various java classes.