Java Notes

Collection Interface

The Collection interface is the parent of the List and Set interfaces, but not Map.

Assume the following declaration for identifiers in the table below:

Collection coll; boolean b; Object obj; int i; Iterator it;

Returns	Method	Action
Adding objects to a collection
`b =`	`coll.add(obj)`	Adds `obj` to this collection. Returns true if the collection was changed because of the add (eg, it will always be true for adding to a List, but will be false when adding to a Set that already contains this object).
`b =`	`coll.addAll(coll)`	Adds all elements of `obj` to this collection. Returns true if the collection was changed because of the addition.
Removing objects from a collection
	`coll.clear()`	Removes all elements from the collection.
`b =`	`coll.remove(obj)`	Removes one occurrence of `obj` from this collection. Returns true if the collection was changed because of this operation.
`b =`	`coll.removeAll(coll)`	Removes all elements of `coll` from this collection. Returns true if the collection was changed because of this operation.
`b =`	`coll.retainAll(coll)`	Removes all elements of which are not in `coll` from this collection. Returns true if the collection was changed because of this operation.
Testing for presence in a collection
`b =`	`coll.contains(obj)`	Returns true if `obj` is in this collection.
`b =`	`coll.containsAll(coll)`	Returns true if all the members of `coll` are in this collection.
`b =`	`coll.isEmpty()`	Returns true if there are no objects in this collection.
Other
`it =`	`coll.iterator()`	Returns an iterator for this collection. The order of elements is only specified if the underlying collection has an ordering (eg, List and TreeSet so, HashSet doesn't).
`i =`	`coll.size()`	Returns the number of objects in this collection.
`Object[] =`	`coll.toArray()`	Returns an array containing the elements of this collection.
`Object[] =`	`coll.toArray(Object[])`	Returns an array containing the elements of this collection.