question: public Comparable < ? > [ ] toArray ( Comparable < ? > [ ] data ) { if ( data == null ) { data = new Comparable < ? > [ size ( ) ] ; } if ( data . length != size ( ) ) { throw new IllegalArgumentException ( MessageFormat . format ( "Array of size {0,number,integer} does not match {1,number,integer} elements." , data . length , size ( ) ) ) ; } for ( int i = 0 ; i < data . length ; i ++ ) { data [ i ] = get ( i ) ; } return data ; }
target:  Converts the data column to an array.