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;
    }

    // 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;
    }

    // ✅ 修复后的静态 swap 方法
    public static <K, V> Pair<V, K> swap(Pair<K, V> pair) {
        return new Pair<>(pair.getValue(), pair.getKey());
    }

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