[ajug-members] Classes Interfaces Constructor

[Joe Sam Shirah]

    Hi Berlin,

> I am trying to figure how constructors are implicitly called, for example.

    See the Java Language Specification at

"8.8.5 Constructor Body"

<http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#784
35>

and

8.8.7 Default Constructor

<http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#168
23>

>And are there ways to force an implementation of a
> constructor(adding 'abstract')

    Not sure what you mean by the statement above.

> but what about

>    public B() {

>       // is super() implicitly added here? which calls blah()

>    }

    From the spec above, the answer is yes.

> or
>   public B(String x) {
>      // is super(x) implicitly added here also, which calls
another_blah();?
>   }

    Never happen.  Only implicit calls to the default, no arg constructor
are added if no explicit super constructor is invoked.

    There was a recent question about instance initializers at the Java
Filter Forum, and I found an article by Dick Baldwin that, while it does not
really talk about implicit, default constructors, is very helpful in
understanding the construction/initialization process.  See

The Essence of OOP using Java, Instance Initializers

http://www.developer.com/java/other/article.php/3065621


                                                         Joe Sam

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----- Original Message -----
From: "Berlin Brown" <bbrown at khafra.com>
To: <ajug-members at ajug.org>
Sent: Thursday, June 10, 2004 11:00 AM
Subject: [ajug-members] Classes Interfaces Constructor


I am reading the docs on Constructors and I am trying to figure how
constructors are implicitly called, for example.
And are there ways to force an implementation of a constructor(adding
'abstract')

public class A {

   public A() {
      blah();
   }

   public A(String val) {
     another_blah();
   }
}

public class B extends A {

   public B() { super();  <-- of course this calls blah() above
   }

but what about

    public B() {

       // is super() implicitly added here? which calls blah()

    }

or
   public B(String x) {
      // is super(x) implicitly added here also, which calls
another_blah();?
   }


}


Berlin Brown
bbrown at khafra.com
(404)979-6999
ext. 7260