Question

I have following class. In this, Iris is another class with some attributes.

public class Helper {

    Iris iris;
    double distance;

    public Helper(Iris iris, double distance) {
        this.iris = iris;
        this.distance = distance;
    }
}

I want to sort an array list of this (i.e List < Helper > helperList), descending based on distance parameter. I have written the following method but it is not working.

public void sort(){
for(int k=0; k < helperList.size(); k++)
        {
            double distance = helperList.get(k).distance; 

             for(int l=0; l < helperList.size(); l++)
             {
                 Helper temp = helperList.get(l);
                 if( distance < temp.distance )
                 {
                     helperList.set(l, helperList.get(k));
                     helperList.set(k, temp);
                 }
            }
        }
}

Can anybody suggest a solution?

Answer 1

Why don’t you get your Helper class to implement Comparable interface and then use the in-built sort method offered by the Collections class.

Collections.sort(helperList) 

I think that would solve the problem. Plus, this sort method is stable.

http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#sort%28java.util.List%29

http://docs.oracle.com/javase/7/docs/api/java/lang/Comparable.html

Implementing Comparable interface:

public class Helper implements Comparable{

    Iris iris;
    double distance;

    public Helper(Iris iris, double distance) {
        this.iris = iris;
        this.distance = distance;
    }

    public int compareTo(Helper other) {
        return new Double(this.distance).compareTo(new Double(other.distance));

    }
}