code: public Object put(Object key, Object value) {
          if (key instanceof Number) {
              return put( ((Number)key).intValue(), value );
          }
          else {
              throw new UnsupportedOperationException
                  ("IntHashMap key must be a number");
          }
      }
docs: Associates the specified value with the specified key in this map.
  If the map previously contained a mapping for this 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 previous value associated with specified key, or <tt>null</tt>
  if there was no mapping for key.  A <tt>null</tt> return can
  also indicate that the IntHashMap previously associated
  <tt>null</tt> with the specified key.