code: public boolean containsKey(int key) {
          Entry tab[] = table;
  
          int index = (key & 0x7FFFFFFF) % tab.length;
          for (Entry e = tab[index]; e != null; e = e.next) {
              if (e.key == key) {
                  return true;
              }
          }
          
          return false;
      }
docs: Returns <tt>true</tt> if this map contains a mapping for the specified
  key.
  
  @return <tt>true</tt> if this map contains a mapping for the specified
  key.
  @param key key whose presence in this Map is to be tested.