Gratuitious constructor

[Vladas Razas]

From C++ I remember Meyers rule "Avoid gratuitious constructors". I forgot why? What terrible things may happen?

Vladas

[Vladas Razas]

I am interested in Java context... Are these still bad in Java?

[Udayan Patel]

Originally posted by Vladas Razas:
From C++ I remember Meyers rule "Avoid gratuitious constructors". I forgot why? What terrible things may happen?

Vladas

http://home.earthlink.net/~huston2/dp/init.html

[Vladas Razas]

There is no initializer lists in Java. In C++ there are reasons to avoid gratuitious constructors, but how about Java? Aren't we still typing

public SomeClass() {
}

for no reason?

[Stan James]

I'd see it more a design decision than a blanket statement. If you create an object via the default constructor, is it truly useful yet? Or is it in an invalid state because some member variables are not yet filled in? The answers are both "it depends." You'll have to answer this on a per-object basis.

There are a lot of benefits to immutable objects that are fully initialized by the constructor and have no methods to change any state. Search for past discussions of immutable String for more details.

[Vladas Razas]

No, I dont argue about constructor's purpose I am just asking if explicitly typing default constructor with no params and no functionality is "a good" style in Java as it was in C++ .

[Joe Borderi]

"From C++ I remember Meyers rule "Avoid gratuitious constructors". I forgot why? What terrible things may happen?"

Actually, the rule is "Avoid gratuitous default constructors."

Briefly, Meyers's reasoning is that an object may not have all the information to be fully initialized if the object is constructed through its default constructor. For example, an Employee class may take an EmployeeID as a constructor argument. The Employee object is really incomplete without that EmployeeID. In this context, I think the "avoid gratuitous constructors" rule also applies to Java.

The term "default constructor", however, opens up a hole in another can of worms when applied to Java. Java programmers seem to use the term "default constructor" to mean only the compiler gernerated constructor.

[Vladas Razas]

So if my class is fully initialized and ready to use without any special steps, then it's not bad if I do not write any constructor?

[Ilja Preuss]

Originally posted by Vladas Razas:
So if my class is fully initialized and ready to use without any special steps, then it's not bad if I do not write any constructor?

Exactly.

[Warren Dew]

J Borderi:

Actually, the rule is "Avoid gratuitous default constructors."

Briefly, Meyers's reasoning is that an object may not have all the information to be fully initialized if the object is constructed through its default constructor. For example, an Employee class may take an EmployeeID as a constructor argument. The Employee object is really incomplete without that EmployeeID. In this context, I think the "avoid gratuitous constructors" rule also applies to Java.

Right. And in Java, if you write no constructor at all, that means there is a default constructor that may or may not be gratuitous - people can still call the automatically generated one even if you haven't written it. For that reason, I think it's best to explicitly write the default constructor if you intend for it to be used - and for safety, if the compiler will generate a default constructor that you don't want used, write it and make it private to enforce that.

[Edwin Keeton]

The compiler will not generate a default constructor if you write your own constructor (with or without parameters).