Properly removing an Integer from a List<Integer>

Question

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

List<Integer> list = new ArrayList<Integer>();

list.add(5);

list.add(6);

list.add(7);

list.add(1);

Any educated guess on what happens when you execute list.remove(1)? What about list.remove(new Integer(1))? This can cause some nasty bugs.

What is the proper way to differentiate between remove(int index), which removes an element from given index and remove(Object o), which removes an element by reference, when dealing with lists of integers?

Answer 1

Java always calls the method that best suits your argument. Auto boxing and implicit upcasting is only performed if there's no method which can be called without casting / auto boxing.

The List interface specifies two remove methods (please note the naming of the arguments):

• remove(Object o)
• remove(int index)

That means that list.remove(1) removes the object at position 1 and remove(new Integer(1)) removes the first occurrence of the specified element from this list.