Sorting arrayList in java based on user input

Question

I have the following class.

class{
        String name;
        int marks;
};

Now i have to sort the objects either alphabetically(names) or descending(marks),based on user input. How to write the comparator function for this. User will enter 'n' to sort using names and 'm' to sort using marks.

Either pass the user input to the comparator or select a comparator based on user input (probably the better way to do it). — Thomas, Mar 29 '16 at 09:04
I am new to Java, and just studied ArrayList, so i'm not sure how to start. — Souvik, Mar 29 '16 at 09:05

Sumit Singh · Answer 1 · 2016-03-29T09:17:02.513

1

Create two Comparator<> one for names another for marks and based on your user input choose one and perform following.

Collections.sort(yourList, yourComparator);

See sort(List<T> list, Comparator<? super T> c))

public class YourFirstComparator implements Comparator<YourClass> {
    @Override
     public int compare(YourClass o1, YourClass o2) {
        // your logic to return 
        // -1 if o1 is small, 1 is o1 is greater, 0 if both are equals
        return  yourValue

    }
}

edited Mar 29 '16 at 09:17

answered Mar 29 '16 at 09:06

Sumit Singh

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how may these comparators look like? – Alex Salauyou Mar 29 '16 at 09:13
@SashaSalauyou see the updated answer – Sumit Singh Mar 29 '16 at 09:17
I meant, that there are `name` and `makrs` variables in OP class already, so they may be just `Comparator.comparing(e -> e.name)` and `Comparator.comparing(e -> -e.marks)` – Alex Salauyou Mar 29 '16 at 09:20
See some example here https://examples.javacodegeeks.com/core-java/util/comparator/java-comparator-example/ – Sumit Singh Mar 29 '16 at 09:27

Sorting arrayList in java based on user input

1 Answers1