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

    // 构造方法
    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }

    // 交换方法：交换 key 和 value 的值
    public Pair<V, K> swap() {
        return new Pair<>(value, key);
    }

    // Getter/Setter
    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;
    }

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

    // 测试
    public static void main(String[] args) {
        Pair<String, Integer> pair = new Pair<>("年龄", 20);
        System.out.println("交换前：" + pair);
        Pair<Integer, String> swapped = pair.swap();
        System.out.println("交换后：" + swapped);
    }
}