JAVA: Implementing the Singleton Design Pattern for Creating a Single Instance with Example

Implementing the Singleton Design Pattern helps in creating only a single instance of a class. Below is a simple example for better understanding.

Class with Main Function

// Class with Main function for calling Singleton class
public class TestSingleTon {

    public static void main(String[] args) {
        SingleTonClass classInstance = SingleTonClass.getInstance();

        System.out.println(
            "My SingleTon member value is=" + classInstance.testval
        );
    }
}

Singleton Class

// Singleton class
public class SingleTonClass {

    // Create an instance
    private static SingleTonClass my_instance = new SingleTonClass();

    // Private constructor
    private SingleTonClass() {
        // Private Constructor here
        // Does not allow an object to be created outside this class
    }

    // Method to access the instance
    public static SingleTonClass getInstance() {
        return my_instance;
    }

    // Member variable
    int testval = 10;

    // If the comment is removed from the below line,
    // the program will not compile.
    // SingleTonClass s1 = new SingleTonClass();
}

Output

The output of this program is:

My SingleTon member value is=10

This is a simple implementation of the Singleton Design Pattern that ensures only one object is created.

There are also other ways to implement the Singleton Design Pattern, such as lazy initialization, thread-safe implementation, and handling Singleton instances across multiple JVMs.