Java- Constructors

class Constructors {
    public static void main(String[] args) {
        Greet g = null; //local variable should be initialized before use
        if (args.length != 0) {
            g = new Greet(args[0]);
        } else {
            /*provided to avoid NullPointerException when no command line
             argument is given*/
            g = new Greet();
        }
        g.showGreeting();

    }
}

class Greet {
    private String name = "Anonymous";

    Greet() { //provided to ensure the success of g = new Greet(); 
    }
    /*if not given: 
    cannot find symbol
    symbol : constructor Greet()*/

    Greet(String name) {
        /*refining the scope of instance variable name using the predefined reference variable this since, its direct usage refers only to the local variable name*/
        this.name = name;
    }

    void showGreeting() {
        System.out.println("Hi " + name + "!!!");
    }
}

Case Study:

java Constructors
Hi Anonymous!!!

java Constructors uce
Hi uce!!!

Note: Default constructor is provided by the Java Virtual Machine(JVM) only when a class does not have one of its own.