Pair.java

package com.bazlur.ds;

/**
 * @author Bazlur Rahman Rokon
 * @since 7/12/17.
 */
public class Pair<T, U> {
    private final T x;
    private final U y;

    private Pair(T x, U y) {
        this.x = x;
        this.y = y;
    }

    public T getX() {
        return x;
    }

    public U getY() {
        return y;
    }

    public static <T, U> Pair<T, U> of(T x, U y) {
        return new Pair<>(x, y);
    }

    @Override
    public String toString() {
        return "(" + x + "," + y + ')';
    }
}

PairDemo.java

package com.bazlur.ds;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author Bazlur Rahman Rokon
 * @since 7/12/17.
 */
public class PairDemo {

    public static void main(String[] args) {

        Map<Integer, List<Pair<Integer, Integer>>> map = new HashMap<>();


        List<Pair<Integer, Integer>> pairs = Arrays.asList(Pair.of(3, 2), Pair.of(3, 4), Pair.of(6, 7));
        List<Pair<Integer, Integer>> pairs2 = Arrays.asList(Pair.of(4, 2), Pair.of(1, 4), Pair.of(4, 7));

        map.put(1, pairs);
        map.put(2, pairs2);

        System.out.println(map);
    }
}