Program/Source Code:

The source code to compare instances of the singleton class is given below. The given program is compiled and executed successfully.

// Java program to compare instances of Singleton class

class Singleton {
  private static Singleton singleRef = null;

  private Singleton() {}

  public static Singleton getSingletonInstance() {
    if (singleRef == null)
      singleRef = new Singleton();

    return singleRef;
  }
}

class Main {
  public static void main(String args[]) {
    Singleton obj1 = Singleton.getSingletonInstance();
    Singleton obj2 = Singleton.getSingletonInstance();
    Singleton obj3 = Singleton.getSingletonInstance();

    if (obj1 == obj2 && obj1 == obj3)
      System.out.println("All objects are pointing to the same memory location.");
    else
      System.out.println("All objects are not pointing to the same memory location.");
  }
}

Output:

All objects are pointing to the same memory location.

Explanation:

In the above program, we created a singleton class Singleton and public class Main. The Singleton class contains a method that returns the instance of class.

The Main class contains a static method main(). The main() is an entry point for the program. And, created the instances obj1, obj2, obj3 and compared all objects, and printed the appropriate message.