Map collection
Overview and Features Map collection:
A: Overview
The key value mapped to the object
A map can not contain duplicate keys
Each key can map up to a value
B: Map of different interfaces and interface Collection
Map is a two-column, Collection is a single row
Unique, Collection sub-system Set Map is unique
Map data structure value for a set of valid keys, nothing to do with value; data structures Collection is a set of elements for effective
Map collection features overview:
a: add functionality
V put (K key, V value): additive element
If the key is first stored, the direct memory element, return null
If the key is not the first store to replace the previous value with the value and returns the previous value
b: delete function
void clear (): Removes all of the elements key
V remove (Object key): The key to delete the key element, and returns the value
c: determining function
boolean containsKey (Object key): determining whether the collection contains a specified key
boolean containsValue (Object value): determining whether the collection contains a specified value
boolean isEmpty (): determines whether the set is empty
d: acquisition function
Set<Map.Entry<K，V>> entrySet（）：
V get (Object key): Gets the value according to the key
Set <K> keySet (): Get the set of all keys in the set
Collection <V> values (): Gets a collection of all the worthy collection
e: length Function
int size (): returns the set number of key-value pairs