New to Java

I am creating a program that has two balls which produce a sound when bouncing off the walls and each other. I am having trouble when they collide with each other, as my value for when they hit each other does not seem to be working. Here is my source code :

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.*;
import java.applet.AudioClip;
import java.awt.event. *;

public class BallBouncing extends Applet implements Runnable {
        int x_pos = 20;
        int y_pos = 100;
        int x_speed = 1;
        int y_speed = 1;
        int x1_pos = 70;
        int y1_pos = 130;
        int x1_speed = 1;
        int y1_speed = 1;
        int appletsize_x = 300;
        int appletsize_y = 200;
        int radius = 20;
        int pos = (x_pos - x1_pos)*(x_pos - x1_pos) + (y_pos - y1_pos)*(y_pos - y1_pos);
        double pos1 = Math.sqrt(pos);        
        public AudioClip sound1, sound2;        
        Thread t;
        Button b1 = new Button("Reverse Direction");
        
        public void init() {
            
            b1.addActionListener(new B1());            
            add(b1);
        }
        
        class B1 implements ActionListener {
        public void actionPerformed(ActionEvent e) {
        x_speed = +3;
        y_speed = -3;
        }
        }

        public void start() {
                
                        t = new Thread(this);
                        t.start();
                }
        

        public void stop() {
                
        }

        public void paint(Graphics g) {
                g.setColor (Color.blue);
                g.fillOval(x_pos - radius, y_pos - radius, 2 * radius, 2 * radius);
                g.fillOval(x1_pos - radius, y1_pos - radius, 2 * radius, 2 * radius);
        }

        public void run() {
        
                sound1 = getAudioClip( getDocumentBase(), "Audio1.au" );
                sound2 = getAudioClip( getDocumentBase(), "Audio2.au" );
        
        
                while (true) {
                    try {
                        Thread.sleep(20);
                    } catch (InterruptedException e) {}
                    
                    if (x_pos > appletsize_x - radius)
                    {
                        x_speed = -3;
                        sound2.play();
                        
                    }
                        
                    else if (x_pos < radius)
                    {
                        x_speed = +3;
                        sound2.play();
                    }                   
                  
                    else if (y_pos > appletsize_y - radius)
                    {
                        y_speed = -3;
                        sound2.play();
                    }
                    
                    else if (y_pos < radius)
                    {
                        y_speed = +3;
                        sound2.play();
                    }
                    
                    else if (x1_pos > appletsize_x - radius)
                    {
                        x1_speed = -3;
                        sound2.play();
                    }
                    
                    else if (x1_pos < radius)
                    {
                        x1_speed = +3;
                        sound2.play();
                    }
                    
                    
                    else if (y1_pos > appletsize_y - radius)
                    {
                        y1_speed = -3;
                        sound2.play();
                    }
                    
                    else if (y1_pos < radius)
                    {
                        y1_speed = +3;
                        sound2.play();
                    }
                    
                    else if (pos1 < 40)
                    {
                        x_speed = -3;
                        x1_speed = +3;
                        y_speed = -3;
                        y1_speed = +3;
                        sound1.play();
                    }
                    
                    
                        x_pos += x_speed;
                        y_pos += y_speed;
                        x1_pos += x1_speed;
                        y1_pos += y1_speed;
                        repaint();
                }
        }
}

Any help would be appreciated, thanks.