java/w8/Pair.java

import java.util.HashMap;
import java.util.Map;

public class Pair<K, V> {
    private K first;
    private V second;

    public Pair(K first, V second) {
        this.first = first;
        this.second = second;
    }

    public K getFirst() {
        return first;
    }

    public V getSecond() {
        return second;
    }

    public Pair<V, K> swap() {
        return new Pair<>(second, first);
    }

    @Override
    public String toString() {
        return "Pair{" + first + ", " + second + "}";
    }
}

class Cache<K, V> {
    private final Map<K, V> cache;

    public Cache() {
        this.cache = new HashMap<>();
    }

    public void put(K key, V value) {
        cache.put(key, value);
    }

    public V get(K key) {
        return cache.get(key);
    }

    public V remove(K key) {
        return cache.remove(key);
    }

    public void clear() {
        cache.clear();
    }

    public boolean containsKey(K key) {
        return cache.containsKey(key);
    }

    public int size() {
        return cache.size();
    }

    public boolean isEmpty() {
        return cache.isEmpty();
    }
}