java/src/w8/Main.java

package w8;
 public class Main {
    public static void main(String[] args) throws InterruptedException {
        // Pair test
        Pair<String, Integer> pair = new Pair<>("age", 25);
        System.out.println("Original: " + pair);
        System.out.println("Swap: " + pair.swap());

        // Cache test
        Cache<String, String> cache = new Cache<>(3000);
        cache.put("name", "Ahmed");
        System.out.println("Cache get: " + cache.get("name"));
    }
}

class Pair<K, V> {
    private K key;
    private V value;
    public Pair(K key, V value) { this.key = key; this.value = value; }
    public Pair<V, K> swap() { return new Pair<>(value, key); }
    public String toString() { return "Pair{" + key + "," + value + "}"; }
}

class Cache<K, V> {
    private java.util.HashMap<K, CacheEntry<V>> cache = new java.util.HashMap<>();
    private long defaultExpireTime;
    public Cache(long t) { this.defaultExpireTime = t; }
    public void put(K key, V value) {
        cache.put(key, new CacheEntry<>(value, defaultExpireTime > 0 ? System.currentTimeMillis() + defaultExpireTime : 0));
    }
    public V get(K key) {
        CacheEntry<V> entry = cache.get(key);
        if (entry == null || (entry.expireTime > 0 && System.currentTimeMillis() > entry.expireTime)) return null;
        return entry.value;
    }
    private static class CacheEntry<V> {
        V value; long expireTime;
        CacheEntry(V v, long e) { value = v; expireTime = e; }
    }
}