Why all AbstractList subclasses overrides contains method again?

All,

I have a small query which i could not understand.

Today i was going through sourcecode of java.util package and had a little doubt.

Why all AbstractList subclasses overrides contains method again?

For example:

Source Code for contains method in AbstractCollection class.

public boolean contains(Object o) {
 Iterator<E> e = iterator();
 if (o==null) {
     while (e.hasNext())
  if (e.next()==null)
      return true;
 } else {
     while (e.hasNext())
  if (o.equals(e.next()))
      return true;
 }
 return false;
    }

SourceCode for overrided contains() method for ArrayList subclass.Similarly other subclasses have their own implementation version.

public boolean contains(Object elem) {
 return indexOf(elem) >= 0;
    }
 
public int indexOf(Object elem) {
 if (elem == null) {
     for (int i = 0; i < size; i++)
  if (elementData[i]==null)
      return i;
 } else {
     for (int i = 0; i < size; i++)
  if (elem.equals(elementData[i]))
      return i;
 }
 return -1;
    }

Please can anyone try to explain why the need to override instead of use the superclass implementation directly.

I predict it is because of of performance gain we may achieve when we iterate through indexing?