Re: collection of a class
- From: Lew <lew@xxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 31 Mar 2007 11:43:54 -0400
"ros" <ros...@xxxxxxxxx> wrote:
I am working on this exercise where I have to add a method to a class
that returns 'collections' of another class.
Can anybody explain how I can do it?
Since you admit that it's homework, I am happy to provide hints.
First, let's be very precise about terminology. Did you want collections (no quotes needed) of classes, or instances of classes (i.e., objects)? The first cannot be done, but you can make collections of Class objects. All Java collections are collections of objects.
Second, you should know that the collections classes and just about everything else in the Java world is heavily documented, and where to find the documentation. The Sun tutorials
<http://java.sun.com/docs/books/tutorial/index.html>
and API documentation
<http://java.sun.com/javase/6/docs/api/>
are two of your best resources, and of course, GIYF.
For collections, both the tutorials and the API docs give a good introduction:
<http://java.sun.com/docs/books/tutorial/collections/index.html>
<http://java.sun.com/javase/6/docs/technotes/guides/collections/overview.html>
For how to return something from a method, see
<http://java.sun.com/docs/books/tutorial/java/javaOO/returnvalue.html>
Now let us try something - start with a collection of some type of object:
Collection <SomeType> coll = new HashSet <SomeType> ();
This line or one similar to it might appear somewhere inside the method you are writing.
Somewhere further down in that method you will have a line something like
coll.add( someTypeThing );
and further down still,
return coll;
You will have written the method signature to signal that the return type is
Collection <SomeType>
(it's in the tutorial how to do that)
and Bob's your uncle.
-- Lew
.
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