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

    public Pair() {
        this(null, null);
    }

    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;
    }

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

    public static <K,V> Pair<V,K> swap(Pair<K,V> pair){
        return new Pair<>(pair.getValue(),pair.getKey());
    }


    // ---------- 测试示例 ----------
    public static void main(String[] args) {
        // 创建不同类型的 Pair 实例
        Pair<String, Integer> pair1 = new Pair<>("age", 25);
        Pair<String, String> pair2 = new Pair<>("name", "Alice");
        Pair<Integer, Double> pair3 = new Pair<>(100, 99.5);

        // 输出初始内容
        System.out.println("pair1: " + pair1);
        System.out.println("pair2: " + pair2);
        System.out.println("pair3: " + pair3);

        // 测试 getter
        System.out.println("pair1 key: " + pair1.getKey() + ", value: " + pair1.getValue());

        // 测试 setter
        pair1.setValue(30);
        System.out.println("修改后 pair1: " + pair1);

        // 泛型方法使用示例：交换两个 Pair 的值（演示泛型灵活性）
        Pair<String, Integer> a = new Pair<>("x", 1);
        System.out.println("交换前: a=" + a );
        Pair<Integer,String> b = swap(a);
        System.out.println("交换后: b=" + b );
    }
}