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How can i break the reference

5 replies on 1 page. Most recent reply: Apr 25, 2003 9:09 AM by Matt Gerrans

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Ken

Posts: 7
Nickname: ken85
Registered: Apr, 2003

How can i break the reference Posted: Apr 22, 2003 10:19 AM
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hello everyone, for my understanding if i set
int size = arrayList.size();
and when i add an addional object to the list..
arrayList.add(anObject);
size will refer to the new arrayList.size();
how can i stop this referring, because i need to get the size at the point of time and compare to the new arrayList.size() later on ..thank yoU!


Ken

Posts: 7
Nickname: ken85
Registered: Apr, 2003

Re: How can i break the reference Posted: Apr 22, 2003 11:22 AM
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opss Sorry i realise tat i am wrong, primitive type does not refer to Object .. or can i rephrase my question, how can i create a new copy of object other than referring

scott

Posts: 1
Nickname: thpopes
Registered: Apr, 2003

Re: How can i break the reference Posted: Apr 22, 2003 4:45 PM
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If you want a list that contains references to all of the objects in you original list you can do the following.

Object a = new Object();
Object b = new Object();
List list = new ArrayList();
list.add(a);
list.add(b);

List l2 = new ArrayList(list);

System.out.println(a.equals(l2.get(0)));
System.out.println(b.equals(l2.get(1)));

If you make any changes to either Object a or Object b (which you can't in the case of the Object class) the changes will be reflected in both lists.

if you want a "disconnected" copy of the first list you will have to extend some effort to "clone" the objects in your list.

Vincent O'Sullivan

Posts: 724
Nickname: vincent
Registered: Nov, 2002

Re: How can i break the reference Posted: Apr 22, 2003 11:51 PM
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> How can i create a new copy of object other than referring?

It sounds like a simple enough thing to want to do. Unfortunately, Java does not make it easy for you. As mentioned above, you need to override the Object.clone() method. A full explanation of the ins and outs of doing so is a bit much to cram into a forum such as this. I suggest you download Bruce Eckel's book 'Thinking in Java' (http://mindview.net/Books/TIJ/DownloadSites) and have a read of Appendix A.

Ken

Posts: 7
Nickname: ken85
Registered: Apr, 2003

Re: How can i break the reference Posted: Apr 25, 2003 8:56 AM
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Thank you for enlightening me!

Matt Gerrans

Posts: 1153
Nickname: matt
Registered: Feb, 2002

Re: How can i break the reference Posted: Apr 25, 2003 9:09 AM
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Josh Bloch's Effective Java book also has really excellent coverage of cloning and copy constructors.

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