Question

Possible Duplicate:
Method has the same erasure as another method in type

In one of my classes I wanted to define these two methods:

private void add(List<ChangeSet> changeSetList) {
    for (ChangeSet changeSet : changeSetList) {
        add(changeSet);
    }
}

private void add(List<Change> changeList) {
    for (Change change : changeList) {
        add(change);
    }
}

Then I get the following error:

Method add(List<Change>) has the same erasure add(List<E>) as another method in type DataRetriever

Why isn´t this allowed? What is the problem with method definitions like that? And what should I do to avoid it? I don´t want to rename one of the methods.

Answer 1

That’s just how the type system of Java “works”. The generics List<Change> and List<ChangeSet> aren’t actually different types. The generic parameters are just hints for the compiler to perform certain checks and certain casts. As far as the JVM and the type system is concerned, though, both types are actually “erased” to List<Object> (or just List if you will), and the two types are really the same, with no internal differences. Therefore, you cannot actually overload on different generics parameters, since as far as overload resolution is concerned, the two types are identical.