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Re: Need help! cloning an object
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Re: Need help! cloning an object


  • Subject: Re: Need help! cloning an object
  • From: LD <email@hidden>
  • Date: Fri, 12 Aug 2005 13:25:54 +1000

Hi there,

On 11/08/2005, at 6:12 PM, Amedeo Mantica wrote:

Hi, this is my problem

I have this variable declarations
--------------------------------------------------------------------
public MyClass variable

/** @TypeInfo MyClass */
public NSMutableArray variableArray;
---------------------------------------------------------------------
and this code...

variable=variableArray.objectAtIndex(i);
---------------------------------------------------------------------
I got an "INCOMPATIBLE TYPES" ERROR

As you should. Java is a strongly typed language and as such assigning objects of type Object to someVariable of SomeTypeOtherThanObject (e.g., MyClass) will cause problems with the compiler. You need a correct cast as Michael points out.


===
Before going any further with WO, I suggest you do your best to get a better understanding of the Java language. Otherwise you'll find the going very tough.
http://java.sun.com/docs/books/tutorial/
http://developer.apple.com/referencelibrary/GettingStarted/GS_Java/ index.html


There are at least two fundamental problems with your understanding from the above code...
1) variable=variableArray.objectAtIndex(i); // IS NOT A CLONE OPERATION!
You need to understand the nature of working with objects. Objects are not primitives. You don't get clones of objects via the assignment operator ('=') but a reference to the object.


2) the "@TypeInfo MyClass" comment tells us that you need to cast all objects that you either remove from, add to, or reference in the array to the type MyClass (or any subtypes thereof). e.g.,
MyClass variable;
variable = ( MyClass )variableArray.objectAtIndex( i );


These are fundamental things about the Java language. Tip: look in the API for the return type of a method. If the return type is not the same type or a subtype of what you want to assign it to - then you'll need to cast.

with regards,
--

LD


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References: 
 >Need help! cloning an object (From: Amedeo Mantica <email@hidden>)

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