Question

The text in the book i am reading states in summary

“Technically, constructors cannot be overidden because they have same name as the current class. New constructors are created instead of being inherited. This system works fine;…”

The part I don’t understand is when they say this:

“when your class’s constuctor methods are called, the constructor methods with the same signature for all your superclasses are also called . Therefore, initialization can happen for all parts of a class you inherit”

What I don’t understand is the same signature section…. It comes accross to me as though all the constructors must have the same signature, and then when you initialize a child class object all it’s super classes will automatically be called instead of having to call super(arg1,arg2) for each sub class…. Is this what they are stating?

Answer 1

when your class’s constuctor methods are called, the constructor methods with the same signature for all your superclasses are also called . Therefore, initialization can happen for all parts of a class you inherit

This is incorrect. First, a note on terminology: constructors are not methods, so the term “constructor methods” does not make any sense.

While it is true that a super class constructor is invoked, it needn’t have the same signature. If a subclass constructor begins with a super class constructor invocation expression such as

class Student extends Person {
    public Student(String name) {
        super(name, Occupation.STUDENT);
    }
}

the superclass constructor matching the argument count and types in invoked. You are completely free which arguments you pass to that constructor.

If the subclass constructor does not begin with a super constructor invocation expression, the compiler will insert a call to the accessible zero-argument constructor of the superclass for you – or raise a compilation error if there is no such constructor.

Sams Teach Yourself Java 2 in 21 Days for now

You are aware that Java 2 is a decade out of date? Any book this old will teach you obsolete stuff, that you would be best served to forget quickly. Why not use a more modern book?