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

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

    // 静态交换方法
    public static <T, U> Pair<U, T> swap(Pair<T, U> p) {
        return new Pair<>(p.getValue(), p.getKey());
    }
}