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LRUCacheEngine.java·Java Spring Boot

Thread-safe LRU Cache implementation using HashMap + Doubly Linked List for O(1) reads and eviction.

package com.kartavya.sda.cache;

import java.util.*;

public class LRUCacheEngine<K, V> {
    private final int capacity;
    private final Map<K, Node<K, V>> map;
    private final Node<K, V> head, tail;

private static class Node<K, V> {
        K key; V value;
        Node<K, V> prev, next;
        Node(K k, V v) { this.key = k; this.value = v; }
    }

public LRUCacheEngine(int capacity) {
        this.capacity = capacity;
        this.map = new HashMap<>();
        this.head = new Node<>(null, null);
        this.tail = new Node<>(null, null);
        head.next = tail; tail.prev = head;
    }

public synchronized V get(K key) {
        Node<K, V> node = map.get(key);
        if (node == null) return null;
        moveToHead(node);
        return node.value;
    }

public synchronized void put(K key, V value) {
        Node<K, V> node = map.get(key);
        if (node != null) {
            node.value = value;
            moveToHead(node);
        } else {
            if (map.size() >= capacity) {
                map.remove(tail.prev.key);
                removeNode(tail.prev);
            }
            Node<K, V> newNode = new Node<>(key, value);
            map.put(key, newNode);
            addNode(newNode);
        }
    }

private void addNode(Node<K, V> node) {
        node.next = head.next; node.prev = head;
        head.next.prev = node; head.next = node;
    }

private void removeNode(Node<K, V> node) {
        node.prev.next = node.next; node.next.prev = node.prev;
    }

private void moveToHead(Node<K, V> node) {
        removeNode(node); addNode(node);
    }
}

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