An illustration of Singleton Design Pattern

SingletonExample.java

/**
 * Singleton is a design pattern by which you create a singleton class that has only one instance
 * at any time
 *
 */
public class SingletonExample {

    private static SingletonExample single_instance = null;

    public String msg;

    /**
     * Making the constructor as private
     */
    private SingletonExample() {
        msg= "Hello World!";
    }

    /**
     * Static method to create instance of Singleton class
     * @return single object of 'SingletonExample' class
     */
    public static SingletonExample getInstance() {
        /**
         * Ensuring only one instance is created
         */
        if (single_instance == null)
            single_instance = new SingletonExample();
        return single_instance;
    }

    public static void main(String[] args) {

        /**
         * Instantiating SingletonExample class with variable 'singletonObject'
         */
        SingletonExample singletonObject = SingletonExample.getInstance();

        System.out.println(singletonObject.msg);

    }

}