Java class hierarchy

Subclass Constructors. This constructor explicitly initializes the cx and cy fields newly defined by PlaneCircle , but it relies on the superclass Circle() constructor to initialize the inherited fields of the class. To invoke the superclass constructor, our constructor calls super(). super is a reserved word in Java.

Subclass Constructors. This constructor explicitly initializes the cx and cy fields newly defined by PlaneCircle , but it relies on the superclass Circle() constructor to initialize the inherited fields of the class. To invoke the superclass constructor, our constructor calls super(). super is a reserved word in Java.

A subclass needs a constructor if the superclass does not have a default constructor (or has one that is not accessible to the subclass). If the subclass has no constructor at all, the compiler will automatically create a public constructor that simply calls through to the default constructor of the superclass.