sorting - Sort same value column by second column using Java Comparator -

i having trouble adding column on sorting have. have list , column info sort follow:

void sortresults(mytablemodel model, list<myresultdetail> list) {     collections.sort(list, new beancomparator(model.getsort(), new comparator<comparable>() {         @override         public int compare(comparable o1, comparable o2) {             if(o1 == null) {                 return -1;             }             else if(o2 == null) {                 return 1;             }             else if(o1.)             else {                 return o1.compareto(o2);             }         }     })); } 

in above code using field name mytablemodel sort result. works fine if sorting on 1 column. trying add sorting based on 2 columns.

for example

class myresultdetail {   private string firstcol;   private string secondcol;   private string thirdcol;   ..... } 

if user want sort secondcol have sort equal secondcol value firstcol.