question: public static Input composite ( List < File > files ) { if ( files . size ( ) == 0 ) return NullInput . INSTANCE ; if ( files . size ( ) == 1 ) return new FileInput ( files . get ( 0 ) ) ; return new CompositeInput ( multiple ( files ) ) ; }
target:  Creates and returns an input composed from the specified files altogether. The resulting input object returns the lines lines of the first file first, then the lines of the second file etc.