Explanation to why two constructors are required - constructor

Question

Unfortunately, I do not feel confident with my understanding of default constructors.
I have searched extensively to find a resource that provides an explanation to adhere to my personal learning curve of the Java language. However, upon completing an assignment, I feel I may not be meeting the assignment criteria due to my own feeling of redundancy to need for a default constructor. This is why i feel like i am misinterpreting the concept of different types of constructors all together.
I have created two constructors as the assignment requires. One that takes in no parameters and initializes instance variables to a default value. And another that takes in parameters to give values to the object variables when the new object is created in the main method.
Why am I creating a default constructor for the object if the default is never used in the main method? Below is a sample of my code:
public class Circle {
private double x; // declaring variable to hold value of x coordinate
private double y; // Variable to hold value of y coordinate
private double r; // Variable to hold value of the radius of a circle
/* default constructor */
Circle() {
x = 0.0;
y = 0.0;
r = 0.0;
}
/* constructor takes in three parameters and sets values for variables x, y, and r */
public Circle(double x, double y, double r) {
this.x = x;
this.y = y;
this.r = r;
}
// test class created for main method
public class TestCircle {
public static void main (String[] args){
Circle c1 = new Circle(2.0,3.0,9.0);
System.out.println();
System.out.println(" A circle object has been created with the following attributes:");
c1.printAttributes();
System.out.println();
System.out.println("The circle is tested for the maximum radius of 8.0...");
c1.setRadius(8.0);
System.out.println();
System.out.println("... since the radius is more than the allowable maximum, the new attributes for the Circle are:");
c1.printAttributes();
System.out.println();
System.out.println("The area of the Circle is " + c1.area());
System.out.println("The Circumference of the circle is " + c1.circumference());
System.out.println();
System.out.println("The origin of the circle is now moved by a specified amount...");
c1.move(6,-7);
System.out.println();
System.out.println("The new attributes of the circle are:");
c1.printAttributes();
System.out.println();
System.out.println("Testing if the point (10,-20) is inside the circle...");
System.out.println();
if (c1.isInside(10,-20)){
System.out.println("The point (10,-20) is inside the circle");
}
else {
System.out.println("The point (10,-20) is not inside the circle");
}
} // end of main
} // end of class

Answer 1

If you don’t use it you should delete it. Sometimes you will need to create empty objects in order to set attributes a posteriori, but if you are not using it at all there is no point to have it

Answer 2

The point of making default constructors is sometimes for back end stuff and is considered a "good programming practice" no you don't use the default constructor here in your main and in fact your code would run just fine with no default constructor comment it out and re run your tester you will see it works fine.