How to sort by two fields in Java and specify sort direction?

Question

I have a list of object i want to sort it using two properties. i have searched on internet and i find this solution in java 8.

class ClassA {
    String var2; 
    String var1;
    // getters and setters
}

List<classA> list;
list.sort(Comparator.comparing(ClassA::getVar1).thenComparing(ClassA::getVar2));

this absolutely works and perfectly, but what I want is to use descending sorting on var2 and ascending sorting on var1.

Answer 1

As simple as adding a reversed ...

list.sort(Comparator.comparing(ClassA::getVar1)
                   .thenComparing(Comparator.comparing(ClassA::getVar2).reversed()));

Answer 2

You need to implement the Comparable interface.

Somtehing like this :

class A implements Comparable{
    @Override public int compareTo(A anObjectA) {
        if (this == anObjectA) return 0;
        int ret = var2.compareTo(anObjectA.var2);
        if(ret == 0)
        ...
    }
}

Answer 3

You could make use of the java comparable interface. Something like this could work:

import java.util.*;  
class classAComparator implements Comparator{  
public int compareTo(classA a,classA b){ 
     int res = a.var2.compareTo(b.var2);
     if(res == 0) { //var2 was the same
          //compare using var1 in descending order
     }
     return res;
 }             

You would use this by running list.sort(new classAComparator())