Representation Independence

• Representation Independence means ensuring that the use of an abstract type is independent of its representation.
• Changes in the representation should have no effect on the code outside the abstract type.

Vector v = new Vector();
List l = new List ();
....
v.copyInto (l.elementData);

• This works as long as the List representation does not change.

class List {
  public Entry getEntry (int i);
}

//we can now write

Entry e = l.getEntry (i);
e.element = x;
...
e.element = y;

• This is also bad because if the represenation changes there might no longer be Entry objects.
• The List class should only use Objects.