- collection of instances: grab bag of instances
- iterate: operate on/visit each instance in a collection
- iterator
  - separate class that keeps track of the iteration
  - use it to access each object in the collection without having to know about the collection's implementation details
- ItemIterator classes
  - for collections required by assignments
  - retrieve items from a collection
  - <Item>Iterator retrieves items of type <Item>
- instance methods
  - return true if there are more items to visit in the collection
    - hasMoreItems()
    - hasNext()
  - return a previously unvisited item from the collection
    - nextItem()
    - getNext()
- can't create your own instances
- get an iterator as part of some pre-defined class
- once hasNext() or hasMoreItems() is false, can't use nextItem() or getNext() anymore without causing an exception
- algorithm: set of steps that can be completed to solve a problem
- pseudo-code: English that looks similar to code, but doesn't really follow the syntax of any real programming language