Least Frequent Used Cache - Java Data Structure

Java examples for Data Structure:Cache

  1. HOME
  2. Java
  3. Data Structure
  4. Cache

Description

Least Frequent Used Cache

Demo Code


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

class LFULeastFrequentUsedCache {

  class CacheEntry {
    private String data;
    private int frequency;

    // default constructor
    private CacheEntry() {
    }/*from   w ww  .  jav a  2  s  . c o  m*/

    public String getData() {
      return data;
    }

    public void setData(String data) {
      this.data = data;
    }

    public int getFrequency() {
      return frequency;
    }

    public void setFrequency(int frequency) {
      this.frequency = frequency;
    }

  }

  private static int initialCapacity;

  private static LinkedHashMap<Integer, CacheEntry> cacheMap = new LinkedHashMap<Integer, CacheEntry>();
  /*
   * LinkedHashMap is used since it has features of both HashMap and LinkedList.
   * Thus, we can get an entry in O(1) and we can iterate over it easily.
   */

  public LFULeastFrequentUsedCache(int initialCapacity) {
    this.initialCapacity = initialCapacity;
  }

  public void addCacheEntry(int key, String data) {
    if (!isFull()) {
      CacheEntry temp = new CacheEntry();
      temp.setData(data);
      temp.setFrequency(0);

      cacheMap.put(key, temp);
    } else {
      int entryKeyToBeRemoved = getLFUKey();
      cacheMap.remove(entryKeyToBeRemoved);

      CacheEntry temp = new CacheEntry();
      temp.setData(data);
      temp.setFrequency(0);

      cacheMap.put(key, temp);
    }
  }

  public int getLFUKey() {
    int key = 0;
    int minFreq = Integer.MAX_VALUE;

    for (Map.Entry<Integer, CacheEntry> entry : cacheMap.entrySet()) {
      if (minFreq > entry.getValue().frequency) {
        key = entry.getKey();
        minFreq = entry.getValue().frequency;
      }
    }

    return key;
  }

  public String getCacheEntry(int key) {
    if (cacheMap.containsKey(key)) // cache hit
    {
      CacheEntry temp = cacheMap.get(key);
      temp.frequency++;
      cacheMap.put(key, temp);
      return temp.data;
    }
    return null; // cache miss
  }

  public static boolean isFull() {
    if (cacheMap.size() == initialCapacity)
      return true;

    return false;
  }


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

    LFULeastFrequentUsedCache lfu = new LFULeastFrequentUsedCache(4);

    lfu.addCacheEntry(1, "A");
    System.out.println(lfu.getCacheEntry(1));
    lfu.addCacheEntry(2, "B");
    System.out.println(lfu.getCacheEntry(1));
    lfu.addCacheEntry(3, "C");
    System.out.println(lfu.getCacheEntry(2));
    System.out.println(lfu.getCacheEntry(3));
    lfu.addCacheEntry(4, "D");

    lfu.addCacheEntry(5, "E");

    System.out.println(lfu.getCacheEntry(1));
    System.out.println(lfu.getCacheEntry(2));
    System.out.println(lfu.getCacheEntry(3));
    System.out.println(lfu.getCacheEntry(4));
    System.out.println(lfu.getCacheEntry(5));

  }

}

Related Tutorials