Concurrent LRU Cache - Java Data Structure

Java examples for Data Structure:Cache

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Description

Concurrent LRU Cache

Demo Code

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;

class LRU<Key, Value> {
  private int size;
  private ConcurrentLinkedQueue<Key> linkedQueue;
  private ConcurrentHashMap<Key, Value> hashMap;

  public LRU(final int size) {
    this.size = size;
    this.linkedQueue = new ConcurrentLinkedQueue<Key>();
    this.hashMap = new ConcurrentHashMap<Key, Value>(size);
  }/*w w w .  j  ava  2s.  c o m*/

  /**
   * Return the Value corresponding to the given Key in the map. return null if
   * key not found.
   * 
   * @param key
   *          - Key
   * @return value - Value
   */
  public Value get(Key key) {
    Value value = hashMap.get(key);
    if (value != null) {
      linkedQueue.remove(key);
      linkedQueue.add(key);
    }
    return value;
  }

  /**
   * Add new Key, Value pair to our Map and Queue. If the Key already exists, move
   * it at the beginning of the queue.
   * 
   * @param key
   *          - Key
   * @param value
   *          - Value
   */
  public synchronized void put(final Key key, final Value value) {
    if (hashMap.containsKey(key)) {
      linkedQueue.remove(key);
    }

    while (linkedQueue.size() >= size) {
      Key oldestKey = linkedQueue.poll();
      if (oldestKey != null) {
        hashMap.remove(oldestKey);
      }

      linkedQueue.add(key);
      hashMap.put(key, value);
    }
  }
}

public class Main{
  public static void main(String arg[]) {

    LRU lru = new LRU(3);

    lru.put(1, 1);
    lru.put(2, 2);
    lru.put(3, 3);
    lru.put(4, 4);
    lru.put(5, 5);

    System.out.println("Data :" + lru.get(1));
    System.out.println("Data :" + lru.get(2));
    System.out.println("Data :" + lru.get(3));
    System.out.println("Data :" + lru.get(4));
    System.out.println("Data :" + lru.get(5));

  }

}

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