CODEWITHSUNDEEP
javaandroid
Gunaseelan
Gunaseelan

Reputation: 15515

Sort function in Java collections

If I have following list of student objects, 

obj1.Name = "ABC";
obj1.Rank = 5;

obj2.Name = "DEF",
obj2.Rank = 3;

obj3.Name = "GHI";
obj3.Rank = 2;

obj4.Name = "JKL";
obj4.Rank = 0;

obj5.Name = "MNO";
obj5.Rank = 1;

obj6.Name = "PQR";
obj6.Rank = 4;

I need to sort these objects in following order.

obj5,
obj3,
obj2,
obj6,
obj1,
obj4.

I have tried following code,

Collections.sort(studentList, new Comparator<Student>() {
    @Override
    public int compare(Student obj2, Student obj1) {
            return obj2.Rank.compareTo(obj1.Rank);
    }
});

I am getting following result.

obj4,//this should be in last position
obj5,
obj3,
obj2,
obj6,
obj1.

But I need all zero's should be at last.

Upvotes: 1

Views: 90

Answers (3)

Michael Anderson
Michael Anderson

Reputation: 73480

A better way to sort them with 0 higher than any value is:

Collections.sort(StudentList, new Comparator<Student>() {
    @Override
    public int compare(Student obj1, Student obj2) {
        if(obj1.Rank==0) return (obj2.Rank==0) ? 0 : 1;
        if(obj2.Rank==0) return -1;
        return Integer.compare(obj1.Rank,obj2.Rank);
    }
});

This will correctly handle the case where obj.Rank=Integer.MAX_VALUE.

If your Ranks are Integers rather than ints you'll also need to handle the case where they're null.

Upvotes: 2

Saurabh Kataria
Saurabh Kataria

Reputation: 81

You can edit compare method , and put a check for zero

Collections.sort(studentList, new Comparator<Student>() {

    @Override
    public int compare(Student obj2, Student obj1) {
    if(obj1.rank ==0 ){
         if(obj2.rank ==0){
          // when both count are zero then you can handle here
         }
        // return positive int beacuse zero is greater than everyother count
      }
    else return obj2.Rank.compareTo(obj1.Rank);
    }
});

Upvotes: 0

Krease
Krease

Reputation: 16215

If you want to put 0's last in sort order, and leave others in ascending order (ie: 1, 2, 3, 4, 5, 0), you'll need to write a custom Comparator that treats 0's as the largest value. Possibly something like this:

Collections.sort(StudentList, new Comparator<Student>() {
    @Override
    public int compare(Student obj1, Student obj2) {
        Integer compareRank1 = obj1.Rank == 0 ? Integer.MAX_VALUE : obj1.Rank;
        Integer compareRank2 = obj2.Rank == 0 ? Integer.MAX_VALUE : obj2.Rank;
        return compareRank1.compareTo(compareRank2);
    }
});

Upvotes: 1

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