Or you can use JavaSound to make audio on your computer.  It uses the
sound card not the PC speaker though.

package javaprojects.classes;

import javax.sound.sampled.*;

public class Tone {
    public static void sound(int hz, int msecs, double vol)
     throws IllegalArgumentException, LineUnavailableException {

        if (vol > 1.0 || vol < 0.0)
            throw new IllegalArgumentException("Volume out of range 0.0
- 1.0");

        byte[] buf = new byte[msecs * 8];

        for (int i=0; i<buf.length; i++) {
            double angle = i / (8000.0 / hz) * 2.0 * Math.PI;
            buf[i] = (byte)(Math.sin(angle) * 127.0 * vol);
        }

        // shape the front and back ends of the wave form
        for (int i=0; i<20 && i < buf.length / 2; i++) {
            buf[i] = (byte)(buf[i] * i / 20);
            buf[buf.length - 1 - i] = (byte)(buf[buf.length - 1 - i] *
i / 20);
        }

        AudioFormat af = new AudioFormat(8000f,8,1,true,false);
        SourceDataLine sdl = AudioSystem.getSourceDataLine(af);
        sdl.open(af);
        sdl.start();
        sdl.write(buf,0,buf.length);
        sdl.drain();
        sdl.close();
    }

    public static void main(String[] args) throws
LineUnavailableException {
        Tone.sound(2000,500,1.0);
    }
}