Java:对具有两种类型的泛型类进行排序

public class Pair<T, U> {
    private T first;
    private U second;

    public Pair(T first, U second) {
        this.first = first;
        this.second = second;
    }

    public T getFirst() {
        return first;
    }

    public U getSecond() {
        return second;
    }
}

import java.util.Comparator;

public class PairComparator implements Comparator<Pair<?, ?>> {
    @Override
    public int compare(Pair<?, ?> pair1, Pair<?, ?> pair2) {
        Comparable<Object> first1 = (Comparable<Object>) pair1.getFirst();
        Comparable<Object> first2 = (Comparable<Object>) pair2.getFirst();
        return first1.compareTo(first2);
    }
}

Pair<Integer, String> pair1 = new Pair<>(3, "Apple");
Pair<Integer, String> pair2 = new Pair<>(1, "Orange");
Pair<Integer, String> pair3 = new Pair<>(2, "Banana");

List<Pair<Integer, String>> pairs = new ArrayList<>();
pairs.add(pair1);
pairs.add(pair2);
pairs.add(pair3);

Collections.sort(pairs, new PairComparator());