List Problem
i have a problem adding a custom object i created into a list
my object is defined as
privatestaticclass PacketType{
int type;
int SeqNum;
int length;
char[] data =newchar[64];
}
I create an instance of this object, modify the insides, and add it to the list. This is done in a loop and the same object is modified and added to the list several times
However once i itirate through the list, only the last object is shown, and is shown as many time as the object was added
WHAT I THINK THE PROBLEM IS
When i add the object into the list, i actually add the address to this object. Since the object is constantly being "Updated" the most recent addition applies to all additions.
Is a way around this? Making every time i add the object to the list, it creates its own object, and isnt changed
Perhaps theres a keyword for the object defenition that insures unique adresses? im stuck
> I create an instance of this object, modify the insides, and add it to the list.
No, you don't :-) Variables in Java do not contain objects. They can contain an object reference (whose value is either null or a pointer to an object).
> Is a way around this? Making every time i add the object to the list, it creates its own object, and isnt changed
No, not as such. What you ought to do is just create a new, separate object in each loop iteration, and add the new reference to the list.
This is nothing specific to lists or collections; it's just the way reference variables and objects are defined in Java.
Lokoa at 2007-7-10 1:56:56 >
> Is a way around this?
Yes.
The solution is simple. Don't do this:
List list = new ArrayList();
PacketType packet = new PacketType ();
while (...) {
//set packet properties
list.add(packet);
}
... because in the end, list will contain may references to the same
PacketType object (think: new PacketType is only called once!)
Instead, simply do this:
List list = new ArrayList();
while (...) {
PacketType packet = new PacketType ();
//set packet properties
list.add(packet);
}
thanks! Now im getting individual references, i know this because the different variables of my custom object reflect the changes, however, this is not the case for my
char[] data = new char[64];
variable. Im certain its a memory referencing problem. Is there a way to tell the object that it should make a new char everytime another object is created?
You can do something like the following:
class PacketType{
private int type;
private int seqNum;
private int length;
private char[] data;
public PacketType(int type, int seqNum, int length, char[] data) {
this.type = type;
this.seqNum = seqNum;
this.length = this.length;
this.data = data.clone();
}
}
If you are using an old (<5) version of Java, that last line should be written:
this.data = (char[]) data.clone();
