a Pair of two values, useful for Streams

Pair.java

package ir.amv.enterprise.laas.webapp.utils.fn;

import lombok.Value;

import java.util.Comparator;
import java.util.Map;
import java.util.function.BiFunction;
import java.util.function.Function;

@Value
public class Pair<K, V> {
    K key;
    V value;

    public <K2> Pair<K2, V> mapKey(Function<K, K2> fn) {
        return new Pair<>(fn.apply(key), value);
    }

    public <V2> Pair<K, V2> mapValue(Function<V, V2> fn) {
        return new Pair<>(key, fn.apply(value));
    }

    public <K2> Pair<K2, V> mapKey(BiFunction<K, V, K2> fn) {
        return new Pair<>(fn.apply(key, value), value);
    }

    public <V2> Pair<K, V2> mapValue(BiFunction<K, V, V2> fn) {
        return new Pair<>(key, fn.apply(key, value));
    }

    public static <K, V> Comparator<Pair<K, V>> comparingKey(Comparator<K> keyComparator) {
        return Comparator.comparing(Pair::getKey, keyComparator);
    }

    public static <K, V> Comparator<Pair<K, V>> comparingValue(Comparator<V> valueComparator) {
        return Comparator.comparing(Pair::getValue, valueComparator);
    }

    public static <K, V> Pair<K, V> fromMapEntry(final Map.Entry<K, V> mapEntry) {
        return new Pair<>(mapEntry.getKey(), mapEntry.getValue());
    }
}