public class Pair<K, V> {
    private final K key;
    private final V value;

    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    public K getKey() {
        return key;
    }

    public V getValue() {
        return value;
    }

    public Pair<V, K> swap() {
        return new Pair<>(this.value, this.key);
    }

    @Override
    public String toString() {
        return "Pair{" + key + " -> " + value + "}";
    }

    public static void main(String[] args) {
        Pair<String, Integer> p1 = new Pair<>("age", 25);
        System.out.println("原始: " + p1);
        Pair<Integer, String> p2 = p1.swap();
        System.out.println("交换后: " + p2);
    }
}