Associates the specified value with the specified key in this map.
If the map previously contained a mapping for the key, the old
value is replaced.
@param key key with which the specified value is to be associated
@param value value to be associated with the specified key
@return the previous value associated with <tt>key</tt>, or
<tt>null</tt> if there was no mapping for <tt>key</tt>.
(A <tt>null</tt> return can also indicate that the map
previously associated <tt>null</tt> with <tt>key</tt>.)
Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replaced.
@param key key with which the specified value is to be associated @param value value to be associated with the specified key @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no mapping for <tt>key</tt>. (A <tt>null</tt> return can also indicate that the map previously associated <tt>null</tt> with <tt>key</tt>.)