collection interfaces vs. collection abstract classes

[love2mao]

Hi Gurus,
I'm studying java 1.4 collection classes. Just notice some confusing interfaces and abstract classes.

java.util contains such interfaces as:

Collection
List
Map
Set

Also, it has some abstract classes. I've thought they're equivalents

AbstractCollection
AbstractList
AbstractMap
AbstractSet

I think interface is enough for us to create some collection-use classes. Why we need AbstrtactXXX? Am I wrong?

For example,

  class myCol implements Collection {
   ...
  }

 
  class myCol extends AbstractCollection{
   ...
  }

Are they the same?

[cma]

They're convience class's. FOr example, the first paragraph in AbstractCollection javadoc is:

This class provides a skeletal implementation of the Collection interface, to minimize the effort required to implement this interface.

.