Collection interface
The root interface in the collection hierarchy. A collection represents a group of objects.
Add elements to a collection
boolean add(E e)- Ensures that this collection contains the specified element (optional operation).
boolean addAll(Collection<? extends E> c)- Adds all of the elements in the specified collection to this collection (optional operation).
Is it contained in the collection
boolean contains(Object o)- Returns true if this collection contains the specified element.
boolean containsAll(Collection<?> c)- Returns true if this collection contains all of the elements in the specified collection.
Compare two collections
boolean equals(Object o)- Compares the specified object with this collection for equality.
Remove elements from a collection
boolean remove(Object o)- Removes a single instance of the specified element from this collection, if it is present (optional operation).
boolean removeAll(Collection<?> c)- Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean retainAll(Collection<?> c)- Retains only the elements in this collection that are contained in the specified collection (optional operation).
Convert collection to Array
Object[] toArray()- Returns an array containing all of the elements in this collection.
<T> T[] toArray(T[] a)- Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
Get the size of a Collection
int size()- Returns the number of elements in this collection.
boolean isEmpty()- Returns true if this collection contains no elements.
Clear a collection
void clear()- Removes all of the elements from this collection (optional operation).
Get the iterator() from a collection
Iterator<E> iterator()- Returns an iterator over the elements in this collection.
Revised from Open JDK source code