The Graphics Class

Every applet's paint(Graphics g) method receives an object of type java.awt.Graphics. That single object is your entire drawing toolkit - it draws text, lines, rectangles, ovals, and polygons onto the applet's surface. Every coordinate you pass is a pixel position measured from the applet's top-left corner: (0, 0) is the top-left, x increases to the right, and y increases downward (not upward, as you might expect from school-level graphs).

drawString - Text

You've already used this one in Your First Applet. It draws a string with its baseline at the given (x, y):

g.drawString("Hello!", 20, 30);

drawLine - Straight Lines

Draws a line between two points, (x1, y1) and (x2, y2):

g.drawLine(20, 50, 120, 50);

drawRect and fillRect - Rectangles

Both take the top-left corner plus a width and height. drawRect draws only the outline; fillRect paints the whole rectangle solid using the current color:

g.drawRect(20, 60, 60, 40);  // outline only
g.fillRect(20, 60, 60, 40);  // solid

There are rounded-corner variants too, drawRoundRect and fillRoundRect, which take two extra arguments for the corner arc's width and height.

drawOval and fillOval - Circles and Ellipses

These also take a bounding box (x, y, width, height) - the oval is drawn inscribed inside that rectangle. Make the width equal to the height and you get a circle:

g.fillOval(100, 60, 40, 40);  // a solid circle, 40x40

drawPolygon - Arbitrary Shapes

For anything with more than four sides, build parallel arrays of x and y coordinates and pass them along with the point count:

int[] xPoints = {200, 230, 260};
int[] yPoints = {100, 60, 100};
g.drawPolygon(xPoints, yPoints, 3);  // a triangle

There is a matching fillPolygon(int[] xPoints, int[] yPoints, int nPoints) for a solid version.

Putting It Together: Extending PaintApplet

Rather than crowd every shape call directly into paint(), pull them into a small private helper method, drawShapes(Graphics g), and call that helper from paint(). This keeps paint() readable as the applet grows more drawing logic in later lessons:

import java.applet.Applet;
import java.awt.Graphics;

public class PaintApplet extends Applet {

    public void init() {
        setBackground(java.awt.Color.WHITE);
    }

    public void paint(Graphics g) {
        g.drawString("Welcome to PaintApplet!", 20, 30);
        g.drawRect(10, 10, getWidth() - 20, getHeight() - 20);
        drawShapes(g);
    }

    private void drawShapes(Graphics g) {
        g.drawLine(20, 50, 120, 50);
        g.drawRect(20, 60, 60, 40);
        g.fillOval(100, 60, 40, 40);
        int[] xPoints = {200, 230, 260};
        int[] yPoints = {100, 60, 100};
        g.drawPolygon(xPoints, yPoints, 3);
    }
}

drawShapes() is marked private because it's an internal implementation detail of PaintApplet, not something any other class needs to call. paint() now reads as a short list of what gets drawn, with the "how" tucked away in the helper.