Getting errors in writing customize sorting for TreeMap in Java

Question

Below is my class Emp and Class Mycomparator which implements Comparator. Both are in same package . I am getting error as The constructor TreeMap(Mycomparator) is undefined. I am new to Java. Please help.

public class Emp {

    String name;
    int eid;

    public Emp(String name, int eid){
        this.name=name;
        this.eid = eid;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Emp e1 = new Emp("shankar",333);
        Emp e2 = new Emp("Ronaldo",222);
        Emp e3 = new Emp("Messi",111);
        TreeMap<Integer,Emp> e = new TreeMap<Integer,Emp>(new Mycomparator());
        e.put(1, e1);
        e.put(2, e2);
        e.put(3, e3);

        Set<Integer> ss = e.keySet();
        for(Integer i:ss) {
            Emp ee = (Emp) e.get(i);
            System.out.println(i+"--------"+ee.eid+"======="+ee.name);
        }
    }
}

Below is my class name Mycomparator which implements Comparator Interface.

public class Mycomparator  implements Comparator<Entry<Integer,Emp>> {

    @Override
    public int compare(Entry<Integer,Emp> arg0, Entry<Integer,Emp> arg1) {
        Map.Entry<Integer,Emp> obj1 = arg0;
        Map.Entry<Integer,Emp> obj2 = arg1;
        Emp e1 = (Emp) obj1.getValue();
        Emp e2 =(Emp) obj2.getValue();
        return  e1.name.compareTo(e2.name); 
        }
    }
}

A `TreeMap` takes a `Comparator` **not** a `Comparator>` - this is your mistake. — Boris the Spider, Sep 25 '16 at 14:14

chrylis -cautiouslyoptimistic- · Answer 1 · 2016-09-25T14:19:57.990

3

A sorted Map is sorted by keys, not values, and the only available option is to sort by the key (Integer), not the "entry". If you want to sort by values, you'll need to write your own map. I'm not aware of any library implementation that sorts by value.

edited Sep 25 '16 at 14:19

answered Sep 25 '16 at 14:13

chrylis -cautiouslyoptimistic-

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Did you mean "values" for that last word? – Andreas Sep 25 '16 at 14:18
There are plenty of questions on this site about sorting a `TreeMap` by value - [for example](https://stackoverflow.com/questions/2864840/treemap-sort-by-value). Might be worth linking one. +1 either way – Boris the Spider Sep 25 '16 at 14:22
@BoristheSpider Except all of them are looking at postprocessing the map by inverting it and sorting then. I didn't want to muddy the (already confused) waters. – chrylis -cautiouslyoptimistic- Sep 25 '16 at 14:22
Some of them work by calling `get` from the `Map` in the `Comparator` - but you're probably right; no need to add more complexity. – Boris the Spider Sep 25 '16 at 14:23

Getting errors in writing customize sorting for TreeMap in Java

1 Answers1