Calling methods from Constructors

[Joel Cochran]

Is it OK to call a classes methods from one of its constructors? I can't think why it wouldn't be but would like some guidance.
I have a class with several instance variables. Some of the variables get populated through a JDBC call to a Database, but I don't want to muck up my constructor code with a lot of this stuff. I also don't want the object to exist without these variables from the database populated, so I thought I'd put the JDBC pieces into a method and let the constructor call that method.
Is this normal? It seems to me that none of the examples I have seen do this...
Thanks

[Rob Ross]

Yes, it's "Ok". Very normal. I do it all the time, for the exact reason you mentioned, to keep your code tidy.
The ONE caveat to remember is that you must be very careful calling polymorphic methods from a constructor, because until the constructor completes running, the object you are creating is not fully instantiated.
For example,

class A {
    String aString = null;
   A() { //constructor 
    somePolymorphicMethod();
    aString = "class A string";
   }
    void somePolymorphicMethod(){
        //do stuff
    }
}
class B extends A{
    int posOfLetterA = 0;
    void somePolyMorphicMethod() { //overriden
    
        posOfLetterA = aString.indexOf("A"); //throws null pointer exception, aString NOT created yet!!
    }
}

Oher than this little gotcha, it's a fine to call other methods.
Rob

[ January 15, 2002: Message edited by: Rob Ross ]

[Dirk Schreckmann]

Hello,
A note for beginners like me who like it spelled out:
In the constructor, you obviously cannot reference properties of the object you are creating until the object's properties have been created. Duh!
[ January 15, 2002: Message edited by: Dirk Schreckmann ]

[Michael Matola]

Originally posted by Rob Ross:
The ONE caveat to remember is that you must be very careful calling polymorphic methods from a constructor, because until the constructor completes running, the object you are creating is not fully instantiated.

I've even seen the recommendation that if you're going to call a class's own instance methods from within its constructor, those methods should be private/final.
[ January 15, 2002: Message edited by: Michael Matola ]

[Joel Cochran]

Thanks everyone!