ques-11-lru-cache.java

/*
 * QUESTION: LRUCache<K,V> — a fixed-capacity cache built on LinkedHashMap
 * using access-order mode plus an overridden removeEldestEntry(), evicting
 * the least-recently-used entry once capacity is exceeded. Used by
 * pro-3-rbac-engine to cache resolved permission sets.
 *
 * Input:  cache of capacity 2: put(1,"a"); put(2,"b"); get(1); put(3,"c")
 * Output: key 2 gets evicted (least recently used), 1 and 3 remain
 */

import java.util.LinkedHashMap;
import java.util.Map;

class LRUCache<K, V> extends LinkedHashMap<K, V> {
  private final int capacity;

  LRUCache(int capacity) {
    super();
    this.capacity = capacity;
  }

  @Override
  protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
    throw new UnsupportedOperationException("TODO");
  }
}

// --- TEST ---
// LRUCache<Integer, String> cache = new LRUCache<>(2);
// cache.put(1, "a"); cache.put(2, "b"); cache.get(1); cache.put(3, "c");
// System.out.println(cache.keySet()); // expected [1, 3]