Currently I am using JDK 1.2.1.

Consider the following simple coding:

import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Stroke;
import java.awt.BasicStroke;
import java.applet.*;


public class Stroke01 extends Applet {

    public void init() {
    }

    public void paint(Graphics g) {

        Graphics2D twoD = (Graphics2D)g;

        BasicStroke pen = new BasicStroke(2.0f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_ROUND);
        twoD.setStroke(pen);
    }
}

When I try to embed the applet to HTML page, it diplays nothing when I run the browser. Why is it happen? Is Graphics2D not supported in JDK 1.2.1? Because whenever I use 2D effect, the actual output will not be displayed.

You are not actually drawing anything in your paint method.. you are just setting the width of your strokes. Add:
twoD.drawString("Hello World", 0, 0);

Ensure your set a size for your applet in your html.

Oh, ya. Thank you so much, Gator.