java collection

添加
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). 
删除
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). 
清空
void clear() 
Removes all of the elements from this collection (optional operation). 
判断
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. 
集合是否为空
boolean isEmpty() 
Returns true if this collection contains no elements. 
获取
size()
Iterator<E> iterator() 
Returns an iterator over the elements in this collection. 
交集
boolean retainAll(Collection<?> c) 
Retains only the elements in this collection that are contained in the specified collection (optional operation). 
转换
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.