Properly removing an Integer from a List

Question

Here\'s a nice pitfall I just encountered. Consider a list of integers:

List list = new ArrayList();
list.add(5);
list.add(6);         


        

Answer 1

Any educated guess on what happens when you execute list.remove(1)? What about list.remove(new Integer(1))?

There is no need to guess. The first case will result in List.remove(int) being called, and the element at position 1 will be removed. The second case will result in List.remove(Integer) being called, and the element whose value is equal to Integer(1) will be removed. In both cases, the Java compiler selects the closest matching overload.

Yes, there is potential for confusion (and bugs) here, but it is a fairly uncommon use-case.

When the two List.remove methods were defined in Java 1.2, the overloads were not ambiguous. The problem only arose with the introduction of generics and autoboxing in Java 1.5. In hind-sight, it would have been better if one of the remove methods had been given a different name. But it is too late now.