Returns the value to which the specified key is mapped,
or {@code null} if this map contains no mapping for the key.
<p>More formally, if this map contains a mapping from a key
{@code k} to a value {@code v} such that {@code key} compares
equal to {@code k} according to the map's ordering, then this
method returns {@code v}; otherwise it returns {@code null}.
(There can be at most one such mapping.)
<p>A return value of {@code null} does not <em>necessarily</em>
indicate that the map contains no mapping for the key; it's also
possible that the map explicitly maps the key to {@code null}.
The {@link #containsKey containsKey} operation may be used to
distinguish these two cases.
@throws ClassCastException if the specified key cannot be compared
with the keys currently in the map
@throws NullPointerException if the specified key is null
and this map uses natural ordering, or its comparator
does not permit null keys
Returns the value to which the specified key is mapped, or {@code null} if this map contains no mapping for the key.
<p>More formally, if this map contains a mapping from a key {@code k} to a value {@code v} such that {@code key} compares equal to {@code k} according to the map's ordering, then this method returns {@code v}; otherwise it returns {@code null}. (There can be at most one such mapping.)
<p>A return value of {@code null} does not <em>necessarily</em> indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to {@code null}. The {@link #containsKey containsKey} operation may be used to distinguish these two cases.
@throws ClassCastException if the specified key cannot be compared with the keys currently in the map @throws NullPointerException if the specified key is null and this map uses natural ordering, or its comparator does not permit null keys