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==null ? k==null :
key.equals(k))}, then this method returns {@code v}; otherwise
it returns {@code null}. (There can be at most one such mapping.)
<p>If this map permits null values, then a return value of
{@code null} does not <i>necessarily</i> 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.
@param key the key whose associated value is to be returned
@return the value to which the specified key is mapped, or
{@code null} if this map contains no mapping for the key
@throws ClassCastException if the key is of an inappropriate type for
this map
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
@throws NullPointerException if the specified key is null and this map
does not permit null keys
(<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)
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==null ? k==null : key.equals(k))}, then this method returns {@code v}; otherwise it returns {@code null}. (There can be at most one such mapping.)
<p>If this map permits null values, then a return value of {@code null} does not <i>necessarily</i> 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.
@param key the key whose associated value is to be returned @return the value to which the specified key is mapped, or {@code null} if this map contains no mapping for the key @throws ClassCastException if the key is of an inappropriate type for this map (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>) @throws NullPointerException if the specified key is null and this map does not permit null keys (<a href="{@docRoot}/java/util/Collection.html#optional-restrictions">optional</a>)