The root interface in the collection hierarchy. A collection represents a group of objects.
Add elements to a collection
| Return | Method | Summary |
|---|---|---|
| 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
| Return | Method | Summary |
|---|---|---|
| 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
| Return | Method | Summary |
|---|---|---|
| boolean | equals(Object o) | Compares the specified object with this collection for equality. |
Remove elements from a collection
| Return | Method | Summary |
|---|---|---|
| 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
| Return | Method | Summary |
|---|---|---|
| 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
| Return | Method | Summary |
|---|---|---|
| int | size() | Returns the number of elements in this collection. |
Is a collection empty
| Return | Method | Summary |
|---|---|---|
| boolean | isEmpty() | Returns true if this collection contains no elements. |
Clear a collection
| Return | Method | Summary |
|---|---|---|
| void | clear() | Removes all of the elements from this collection (optional operation). |
Get the iterator() from a collection
| Return | Method | Summary |
|---|---|---|
| Iterator<E> | iterator() | Returns an iterator over the elements in this collection. |
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