Under "Some rules to remember" 2nd rule is WRONG

The constructor should initialize all instance variables of the object, possibly using some passed parameters.

This is wrong as its not necessary to initialize all the instance variables
if you don’t initialize any instance variable it will be initialized with default value

class Circle {
  public int x;
  public int y;
  public int r;
  public int z;

  public Circle(int initX, int initY, int initR) {
    this.x = initX;
    this.y = initY;
    this.r = initR;

here in the constructor, z is not being initialized and its not wrong.

Hi @Prashant_Kumar_Meena ,

Thank you so much for pointing it out and we have updated the course. Please let us know if you find anything else suspicious.