import java.util.HashMap;
 import java.util.Map;
public class Cache<K, V> {
     private final Map<K, V> cache;
     public Cache() {
         cache = new HashMap<>();
     }
     public synchronized void put(K key, V value) {
         cache.put(key, value);
     }
     public synchronized V get(K key) {
         return cache.get(key);
     }
     public synchronized boolean hasKey(K key) {
         return cache.containsKey(key);
     }
     public synchronized void remove(K key) {
         cache.remove(key);
     }
 }