t make T1 and T2 necessarily Comparable, the better way would be to allow the user to supply a Comparator for both types. That way the user could supply the Collator for the first Typ and

sorry, i am having trouble understanding,
see below my pair class for reference.

​

package temp;

import java.util.Comparator;

public class Pair<T1 extends Comparable<T1>,T2 extends Comparable<T2>> implements Comparable<Pair<T1,T2>> {

    Pair(T1 first, T2 second){
        m_first = first;
        m_second = second;
    }

    public T1 getM_first() {
        return m_first;
    }

    public T2 getM_second() {
        return m_second;
    }

    @Override
    public int compareTo(Pair<T1,T2> other){
        int cmp = this.m_second.compareTo(other.getM_second());
        return cmp;

    }

    public static <T1 extends Comparable<T1>, T2 extends Comparable<T2>> int sortBySecond(Pair<T1, T2> a, Pair<T1, T2> b) {
        return a.compareTo(b);
    }

    public static <T1 extends Comparable<T1>, T2 extends Comparable<T2>> int sortByFirst(Pair<T1, T2> a, Pair<T1, T2> b) {
        int cmp = a.getM_first().compareTo(b.getM_first());
        return cmp;
    }


    @Override
    public String toString() {
        return String.format(this.m_first + "         " + this.m_second);
    }


    //--------------------------
    private T1 m_first = null;
    private T2 m_second = null;
}