Question

So I have an ArrayList in java. And what I’m doing is creating a new list with updated values. But I want to put those new values into the original ArrayList. This is important because I’m passing the original arraylist reference to an object that I no longer have access to, but I need to keep its contents up to date. Is there any way to make java copy the contents into a current reference? I hope that makes sense.

Also, I’d rather not clear the original arraylist and then loop through it pushing the new contents into it.

I need to do something like this:

ArrayList a;
ArrayList *b = a;
//pass b (the pointer) to something
ArrayList c;
*b = c;

I really hope I got that (pseudo) c++ code correct or I’ll look pretty stupid =P

I can see how I’m not being clear, it’s kind of complicated (this is in android so it’s across a couple activities) so let me see if I can get my point across better.

Class1{
ArrayList a;
method1(){

a = Class2.getA();
method_that_uses_a(a);
}
}

Class2{
ArrayList getA(){

ArrayList a = new ArrayList

a = getDataFromWebsite();

return a;
}

Class1's method1() gets called periodically by another portion of code. But I need the reference to a stay the same, but the contents to change to the new contents.

Answer 1

I think your question is unclear, what do you mean by

“And what I’m doing is creating a new list with updated values. But I want to put those new values into the original ArrayList. This is important because I’m passing the original arraylist reference to an object that I no longer have access to, but I need to keep its contents up to date. Is there any way to make java copy the contents into a current reference? I hope that makes sense.”

When you do

List a = new ArrayList
List b = a

you have one ArrayList object, and two references to the object, a and b.

Also note that there is an addAll method that you can use to add members of one collection to another collection. Note that I believe addAll does not do a deep copy, so if you use it both lists have copies of the same reference. So if list a has references a1, a2, a3, and you do b.addAll(a), b now has references to the objects that a1…a3 point to…