Java Reference
In-Depth Information
21.8. Map and SortedMap
The interface Map<K,V> does not extend Collection because it has a con-
tract that is different in important ways. The primary difference is that
you do not add an element to a Map you add a key/value pair. A Map allows
you to look up the value stored under a key. A given key (as defined by
the equals method of the key) maps to one value or no values. A value
can be mapped to by as many keys as you like. For example, you might
use a map to store a mapping of a person's name to their address. If
you have an address listed under a name, there will be exactly one in
the map. If you have no mapping, there will be no address value for that
name. Multiple people might share a single address, so the map might
return the same value for two or more names.
The basic methods of the Map interface are
public int size()
Returns the size of this map, that is, the number of key/value
mappings it currently holds. The return value is limited to In-
teger.MAX_VALUE even if the map contains more elements.
public boolean isEmpty()
Returns TRue if this collection currently holds no mappings.
public boolean containsKey(Object key)
Returns true if the collection contains a mapping for the given
key .
public boolean containsValue(Object value)
Returns TRue if the collection contains at least one mapping to
the given value .
 
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