7.1: Creating Graphics

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There are several ways to create graphics in Java; the simplest way is to use java.awt.Canvas and java.awt.Graphics. A Canvas is a blank rectangular area of the screen onto which the application can draw. The Graphics class provides basic drawing methods such as drawLine, drawRect, and drawString.

Here is an example program that draws a circle using the fillOval method:

import java.awt.Canvas;
import java.awt.Graphics;
import javax.swing.JFrame;

public class Drawing extends Canvas {
    public static void main(String[] args) {
        JFrame frame = new JFrame("My Drawing");
        Canvas canvas = new Drawing();
        canvas.setSize(400, 400);
        frame.add(canvas);
        frame.pack();
        frame.setVisible(true);
    }

    public void paint(Graphics g) {
        g.fillOval(100, 100, 200, 200);
    }
}

The Drawing class extends Canvas, so it has all the methods provided by Canvas, including setSize. You can read about the other methods in the documentation, which you can find by doing a web search for “Java Canvas”.

In the main method, we:

Create a JFrame object, which is the window that will contain the canvas.
Create a Drawing object (which is the canvas), set its width and height, and add it to the frame.
Pack the frame (resize it) to fit the canvas, and display it on the screen.

Once the frame is visible, the paint method is called whenever the canvas needs to be drawn; for example, when the window is moved or resized. The application doesn’t end after the main method returns; instead, it waits for the JFrame to close. If you run this code, you should see a black circle on a gray background.