Returns the value to which this map maps the specified key. Returns
null
if the map contains no mapping for this key. A return value of
null
does not
necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to
null
. The
containsKey
operation may be used to distinguish these two cases.
More formally, if this map contains a mapping from a key k
to a value v
such that (key==null ? k==null : key.equals(k))
, then this method returns v
; otherwise it returns null
. (There can be at most one such mapping.)