Java program to compare instances of singleton class

Learn how to compare instances of singleton class in Java?
Submitted by Nidhi, on March 16, 2022

Problem statement

In this program, we will create a singleton class. Then we will create the objects of the singleton class and compare the instances of the singleton class.

Java program to compare instances of singleton class

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.