public class Pair<K, V> {
    private K key;
    private V value;
    public Pair(K key, V value) {
        this.key = key;
        this.value = value;
    }
    public void swap() {
        K temp = key;
        key = (K)value;
        value = (V)temp;
    }
    public K getKey() { return key; }
    public V getValue() { return value; }
    public static void main(String[] args) {
        Pair<Object, Object> pair = new Pair<>("Name", 18);
        System.out.println("Before swap: key=" + pair.getKey() + ", value=" + pair.getValue());
        pair.swap();
        System.out.println("After swap: key=" + pair.getKey() + ", value=" + pair.getValue());
    }
}