code: public int getRowStart(int rowIndex) {
          if (isCompacted) {
              throw new IllegalStateException(
                      "Illegal Invocation of the method after compact()");
          }
          if (rowIndex < 0 || rowIndex > rows) {
              throw new IllegalArgumentException("rowIndex out of bound!");
          }
          return v[rowIndex * columns];
      }
docs: /*
  Returns an int which is the start codepoint
  in row rowIndex.
  
  @throws IllegalStateException
  
  @throws IllegalArgumentException