Collection Interface

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

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). It appends new element at the end of the list.
b =	coll.addAll(coll)	Adds all elements of obj to this collection. Returns true if the collection was changed because of the addition. It appends new element at the end of the list.
Removing objects from a collection
	coll.clear()	Removes all elements from the collection.
b =	coll.remove(obj)	Removes the specified item from the list for the first 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.

Iterator Interface

Bulk Operations on collections in java

Array Operations on collections in java