Java Question

manolakis · 10-22-2007, 12:14 PM

Hi there
I would be really obliged to anyone that could help me.
I am actually interested in constructing a dynamic object.
To be more clear, if there is an object which has an array of integers as private instance and this array at a given time is full and we want to add one more variable (integer) then we have a "problem".
On the other hand if we have an object with a list as private instance then we can add to that list as much as we want.
As I have seen there are a number of types of Lists in Java(LinkedList, doubleLinkedList, etc). Although that I am really familiar with data-structures in C, it seems that i am really struggling with Java.
I would be happy if anyone could give me an example of constructing such an object.

Thanks

indienick · 10-22-2007, 12:41 PM

If you want simply add one more integer to an "array", you may want to use the java.util.ArrayList<K> class. It's just a class that provides a nice, manageable collection.

Code:

import java.util.ArrayList;
...
...
ArrayList<Integer> ali = new ArrayList<Integer>();
...

I haven't written Java in quite some time, so I can't begin to help you with any of the public instance methods for that class. I also think the syntax for the constructor may have changed slightly...I can't remember. If you're using Eclipse or NetBeans, it'll guide you in the right direction for the constructor syntax.

lamar_air · 10-22-2007, 02:35 PM

If you're looking for an array that can automatically resize then vectors are easy to use for this. They just aren't recommended when performance is a high priority. Just search for "java vector".

manolakis · 10-22-2007, 05:45 PM

Hi and thanks for your replies
I would like to ask something regarding the piece of code that you provided.
Is the following possible?

Quote:

ArrayList<MyObject> ali = new ArrayList<MyObject>();

MyObject of course is a class that we will have created.

indienick · 10-22-2007, 09:29 PM

Absolutely - as long as MyObject implements Object (which EVERYTHING in Java does by default) then you're good!

turbo_spool · 10-22-2007, 09:33 PM

Quote:

Originally Posted by indienick

Absolutely - as long as MyObject implements Object (which EVERYTHING in Java does by default) then you're good!

Thaaats correct!

To add to that: just remember that with Java, the Javadocs are your friend. Big time. When I need to use a class that I am unfamiliar with, my first step is to google.

GOOGLE: java SomeClass class

That usually gets me started.

lamar_air · 10-23-2007, 08:43 AM

By using:

Code:

ArrayList<MyObject> ali = new ArrayList<MyObject>();

instead of:

Code:

ArrayList ali = new ArrayList();

You're using "Generics" which just means that you're only allowing this ArrayList called ali to hold objects of type "MyObject". You can simplify it by not specifying that it must hold MyObjects but it's better practice to specify it like you did. It's better practice because then whoever uses ali knows that it only contains MyObjects..

lamar_air · 10-23-2007, 08:46 AM

More info about generics here: http://java.sun.com/j2se/1.5.0/docs/.../generics.html