Java: ArrayList: Determine if entry exists by its index.

Question

Hello.

How can I check if value exist in ArrayList by its index?

Java offers contains(Object) method, but no contains(Integer index) method

Thank you

Answer 1

Not at all sure what your question is. You talk about seeing if an entry "exists" but then you talk about Java lacking a remove(Object index) method.

Regarding remove: There's the remove(int) method on the List interface implemented by ArrayList. (Java Lists are indexed by int, not by Object.)

Regarding whether an entry "exists" at a given index, if the list's size() method is greater than the index (and the index is non-negative), then there's an entry at that index:

if (index >= 0 && index < list.size()) {
    // An entry exists; hey, let's remove it
    list.remove(index);
}

Answer 2

If you have a sparse array (which can contain null values) you might want to check for this as well.

public static boolean isSet(List<?> list, int index) {
   return index >=0 && index < list.size() && list.get(index) != null;
}

Not sure why you would want the index to be Integer type but if you do you should check for null as well. Allowing a null value is the only good reason to have an Integer type.

public static boolean isSet(List<?> list, Integer index) {
   return index != null && index >=0 && index < list.size() && list.get(index) != null;
}