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.