Set common methods

aggregate ：

Collection Common methods in ：

boolean add(E e); Add objects to the collection ;

boolean addAll(Collection<? extends E> c); Assign parameters to a collection c Add all elements in to the current collection ;

boolean contains(Object o); Determine whether the specified object is included ;

boolean containsAll(Collection<?> c); Determines whether all objects specified by the parameter are included ;

boolean retainAll(Collection<?> c); Keep all objects that exist in the current set and in the parameter set ;

boolean remove(Object o); Remove objects from the collection ;

boolean removeAll(Collection<?> c); Deletes all objects specified by the parameter from the collection ;

void clear(); Empty the set ;

int size(); Returns the number of containing objects ;

boolean isEmpty(); Determine whether it is null ;

boolean equals(Object o) Judge whether it is equal ;

int hashCode() Get the hash code value of the current collection ;

Object[] toArray() Convert collection to array ;

Iterator<E> iterator() Gets the iterator of the current collection ;

Shortcut key ： stay idea Press and hold Ctrl Point method , Jump to the specific content of the method ;Ctrl+n Search and open the source code of the class directly ;Ctrl+F12 Search and open the source code of the method ;

java.util.Iterator Interface ： Used to describe iterator objects , Traversable Collection All elements in the collection , yes Collection Interface's parent class ;

Common methods ：

boolean hasNext() Determine whether there are elements in the set that can be iterated ;

E next() Used to take out one element and point to the next element ;

void remove() Delete the last element accessed ;

abnormal ：

foreach loop ：for( Element type Variable name ： Array / Collection name ）{ The loop body ;}, This method is a simplified version of the iterator ;