basic collection question

[Brian Smith]

This is just a general question

Is this valid?

ObjectFoo o = new ObjectFoo("Foo");
List alist = new ArrayList();
alist.add(o);
 
o = null;
 
for (ObjectFoo foo : alist) {
  System.out.println(foo.toString());
}
 

Is the element o in the arrayList also dereferenced when I set o = null? Or is the object copied when added to the list?

Thanks

[Stan James]

The variable o is a reference to an object. The list has another reference to the same object. When you set o to null or let it go out of scope, the list still has its reference, so the object cannot be garbage collected yet. Did that answer the right question?

BTW: Does that compile? If not, can you fix it?

[Brian Smith]

I don't know if it compiles, it was just "air code" to convey my question. Yes that answers my question, thanks. I didn't think it through enough before I posted. I was getting confused between setting an object reference to null and setting the value of the object to null. The answer is obvious now, Thanks.

-Brian

[Brian Smith]

Ok this compiles (Java 1.5)

import java.util.ArrayList;
 
class test {
 
public static void main(String args[]) {
 
String foo = new String("Test");
ArrayList<String> alist = new ArrayList();
alist.add(foo);
foo = null;
for (String f : alist) {
f.toString();
}
}
}

[Stan James]

Glad you followed it through to compiling. I suspected that your question didn't really require it, but it's cooler this way.