Java集合类
Set:集合中的元素不按某一指定的方式排序，并且不存在重复对象。
List:集合中的元素按索引位置排序,可以有重复对象，支持按照元素在集合中的索引位置查询元素
Map:集合中每一个元素包含一对键对象和值对象，集合中没有重复的键对象，而值对象可以重复。
HashSet 方法
Arraylist方法
boolean add(E e)
Appends the specified element to the end of this list.
void add(int index, E element)
Inserts the specified element at the specified position in this list.
boolean addAll(Collection<? extends E> c)
Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's Iterator.
boolean addAll(int index, Collection<? extends E> c)
Inserts all of the elements in the specified collection into this list, starting at the specified position.
void clear()
Removes all of the elements from this list.
Object clone()
Returns a shallow copy of this ArrayList instance.
boolean contains(Object o)
Returns true if this list contains the specified element.
void ensureCapacity(int minCapacity)
Increases the capacity of this ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument.
E get(int index)
Returns the element at the specified position in this list.
int indexOf(Object o)
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
boolean isEmpty()
Returns true if this list contains no elements.
Iterator<E> iterator()
Returns an iterator over the elements in this list in proper sequence.
int lastIndexOf(Object o)
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
ListIterator<E> listIterator()
Returns a list iterator over the elements in this list (in proper sequence).
ListIterator<E> listIterator(int index)
Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
E remove(int index)
Removes the element at the specified position in this list.
boolean remove(Object o)
Removes the first occurrence of the specified element from this list, if it is present.
boolean removeAll(Collection<?> c)
Removes from this list all of its elements that are contained in the specified collection.
protected void removeRange(int fromIndex, int toIndex)
Removes from this list all of the elements whose index is between fromIndex, inclusive, and toIndex, exclusive.
boolean retainAll(Collection<?> c)
Retains only the elements in this list that are contained in the specified collection.
E set(int index, E element)
Replaces the element at the specified position in this list with the specified element.
int size()
Returns the number of elements in this list.
List<E> subList(int fromIndex, int toIndex)
Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive.
Object[] toArray()
Returns an array containing all of the elements in this list in proper sequence (from first to last element).
<T> T[] toArray(T[] a)
Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.
void trimToSize()
Trims the capacity of this ArrayList instance to be the list's current size
LinkedList方法
boolean add(E e)
Appends the specified element to the end of this list.
void add(int index, E element)
Inserts the specified element at the specified position in this list.
boolean addAll(Collection<? extends E> c)
Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator.
boolean addAll(int index, Collection<? extends E> c)
Inserts all of the elements in the specified collection into this list, starting at the specified position.
void addFirst(E e)
Inserts the specified element at the beginning of this list.
void addLast(E e)
Appends the specified element to the end of this list.
void clear()
Removes all of the elements from this list.
Object clone()
Returns a shallow copy of this LinkedList.
boolean contains(Object o)
Returns true if this list contains the specified element.
Iterator<E> descendingIterator()
Returns an iterator over the elements in this deque in reverse sequential order.
E element()
Retrieves, but does not remove, the head (first element) of this list.
E get(int index)
Returns the element at the specified position in this list.
E getFirst()
Returns the first element in this list.
E getLast()
Returns the last element in this list.
int indexOf(Object o)
Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
int lastIndexOf(Object o)
Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element.
ListIterator<E> listIterator(int index)
Returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list.
boolean offer(E e)
Adds the specified element as the tail (last element) of this list.
boolean offerFirst(E e)
Inserts the specified element at the front of this list.
boolean offerLast(E e)
Inserts the specified element at the end of this list.
E peek()
Retrieves, but does not remove, the head (first element) of this list.
E peekFirst()
Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.
E peekLast()
Retrieves, but does not remove, the last element of this list, or returns null if this list is empty.
E poll()
Retrieves and removes the head (first element) of this list.
E pollFirst()
Retrieves and removes the first element of this list, or returns null if this list is empty.
E pollLast()
Retrieves and removes the last element of this list, or returns null if this list is empty.
E pop()
Pops an element from the stack represented by this list.
void push(E e)
Pushes an element onto the stack represented by this list.
E remove()
Retrieves and removes the head (first element) of this list.
E remove(int index)
Removes the element at the specified position in this list.
boolean remove(Object o)
Removes the first occurrence of the specified element from this list, if it is present.
E removeFirst()
Removes and returns the first element from this list.
boolean removeFirstOccurrence(Object o)
Removes the first occurrence of the specified element in this list (when traversing the list from head to tail).
E removeLast()
Removes and returns the last element from this list.
boolean removeLastOccurrence(Object o)
Removes the last occurrence of the specified element in this list (when traversing the list from head to tail).
E set(int index, E element)
Replaces the element at the specified position in this list with the specified element.
int size()
Returns the number of elements in this list.
Object[] toArray()
Returns an array containing all of the elements in this list in proper sequence (from first to last element).
<T> T[] toArray(T[] a)
Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.
HashMap方法
void clear()
Removes all of the mappings from this map.
Object clone()
Returns a shallow copy of this HashMap instance: the keys and values themselves are not cloned.
boolean containsKey(Object key)
Returns true if this map contains a mapping for the specified key.
boolean containsValue(Object value)
Returns true if this map maps one or more keys to the specified value.
Set<Map.Entry<K,V>> entrySet()
Returns a Set view of the mappings contained in this map.
V get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
boolean isEmpty()
Returns true if this map contains no key-value mappings.
Set<K> keySet()
Returns a Set view of the keys contained in this map.
V put(K key, V value)
Associates the specified value with the specified key in this map.
void putAll(Map<? extends K,? extends V> m)
Copies all of the mappings from the specified map to this map.
V remove(Object key)
Removes the mapping for the specified key from this map if present.
int size()
Returns the number of key-value mappings in this map.
Collection<V> values()
Returns a Collection view of the values contained in this map