Node.java

package lrucache;

/**
 * Doubly-linked list node storing a key-value pair with optional TTL expiry.
 * The key is stored so we can remove it from the HashMap during eviction
 * without a reverse lookup.
 */
public class Node<K, V> {

    final K key;
    V value;
    long expiryMs;          // absolute epoch ms; -1 = no expiry

    Node<K, V> prev;
    Node<K, V> next;

    Node(K key, V value, long ttlMs) {
        this.key = key;
        this.value = value;
        this.expiryMs = (ttlMs > 0) ? System.currentTimeMillis() + ttlMs : -1L;
    }

    /** Returns true if this entry has a TTL and it has elapsed. */
    boolean isExpired() {
        return expiryMs != -1L && System.currentTimeMillis() > expiryMs;
    }
}