A "no-arg constructor" is a constructor with no parameters.
It is good practice to add a no-arg constructor. Especially when your classes get more complex a no-arg constructor can take care of initializing ivars.
Say we have this Rectangle class with the two instance variables shown.
public class Rectangle {
private int width;
private int height;
Here is an example no-arg constructor method. No parameters are passed in to the method, so we simply initialize the ivars to 0.
public Rectangle() {
//Constructing a Rectangle: 0 by 0
this.width = 0;
this.height = 0;
}
Introduction To Objects With Java
(Chapter 406 - Constructors)