Run java script utilizing acm.program package from terminal

I am trying to run the following script - source of code here- on my terminal:

import acm.program.*;

public class Add2 extends Program {

   public void run() {
      println("This program adds two numbers.");
      int n1 = readInt("Enter n1: ");
      int n2 = readInt("Enter n2: ");
      int total = n1 + n2;
      println("The total is " + total + ".");
   }
} 

I then compile and run the code using these two steps on my terminal:

javac -classpath acm.jar Add2.java
java Add2

The compilation indicates no errors , but when I try to run the script, I get the following error: Error: Could not find or load main class Add2. I'm fairly new at working with Java so any advice on how to make this work would be greatly appreciated!

The Java Virtual Machine (JVM) can only execute code with a main method. Code cannot be executed without a main method but it can still be compiled (as you noticed), thus it is mandatory to use a main method or you will run into java.lang.ClassNotFoundException.

Simply add this to your code (you don't need the comments):

public static void main(String[] args) {
    // This class is mandatory to be executed by the JVM.
    // You don't need to do anything in here, since you're subclassing ConsoleProgram,
    // which invokes the run() method.
}

Btw, since you're overriding Program#run() you need to add @Override as annotation. Also, as you're only using the console, subclassing ConsoleProgram would be enough.