Draw the ball and make it move.

Pong.java

+import processing.core.PApplet;
+import java.util.Random;
+
+public class Pong extends PApplet
+{
+    // x position of the ball
+    private int ballX;
+    // y position of the ball
+    private int ballY;
+    // Ball speed in the x direction
+    private int ballSpeedX;
+    // Ball speed in the y direction
+    private int ballSpeedY;
+    // Width of our window
+    final private int width = 640;
+    // height of our window
+    final private int height = 480;
+    
+    public static void main(String[] args) {
+        // Set up the processing library
+        PApplet.main("Pong");
+    }
+
+    public void settings() {
+        // Set our window size
+        size(width, height);
+    }
+
+    public void setup() {
+        // Create a random initial position and speed for the ball
+        Random r = new Random();
+        ballX = r.nextInt(width);
+        ballY = r.nextInt(height);
+        ballSpeedX = r.nextInt(width / 100) + 1;
+        ballSpeedY = r.nextInt(height / 100) + 1;
+    }
+
+    public void draw() {
+        // Clear the background of the window
+        background(255, 255, 255);
+        // Draw the ball
+        ellipse(ballX, ballY, 32, 32);
+        // Move the ball
+        ballX += ballSpeedX;
+        ballY += ballSpeedY;
+    }
+}

pong.sh

+#!/bin/bash
+#PROCESSING=/usr/share/java/processing-core.jar
+PROCESSING=~/Downloads/processing-3.3.5/core/library/core.jar
+javac -cp $PROCESSING Pong.java
+java -cp $PROCESSING:. Pong