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

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

    public K getKey() { return key; }
    public void setKey(K key) { this.key = key; }
    public V getValue() { return value; }
    public void setValue(V value) { this.value = value; }

    // 交换键值的静态方法
    public static <K, V> Pair<V, K> swap(Pair<K, V> pair) {
        return new Pair<>(pair.getValue(), pair.getKey());
    }

    @Override
    public String toString() {
        return "Pair{" + "key=" + key + ", value=" + value + '}';
    }

    public static void main(String[] args) {
        // 测试
        Pair<String, Integer> pair = new Pair<>("age", 18);
        System.out.println("交换前：" + pair);

        Pair<Integer, String> swappedPair = Pair.swap(pair);
        System.out.println("交换后：" + swappedPair);
    }
}