Practice with constructors

The fourth contructor should be: public Circle(Circle oc) { this(oc.x, oc.y, oc.radius); } but instead of it - in solution it is: public Circle(double x) { ...}

Interesting fact: If a class doesn't declare any constructors, the Java compiler automatically provides a default constructor (a no-argument constructor) for us. However, if there is any declared constructor, the compiler will not provide the default one.