Implementing a Least-Recently-Used(LRU) Cache

In this section, you will learn about the least-recently- used(LRU) cache in Java. LRU Cache helps you how to use the buffer and how to limit or fixed the size of buffer and how to manage storing and retrieving process of the buffer which size is limited.

In this section, you can create a LRU(least-recently-used) Cache and manage it efficiently. Here the given program takes a in numeric input to fix the size of the LRU Cache. If your entry exceeds the size of the LRU Cache the the eldest element with key is removed. LRU Cache is implemented through the LinkedHashMap class. LinkedHashMap holds values with unique key. You you store values with a duplicate key then the LinkedHashMap replace the old value of that key with the new value of the key.

Code Description:

This program shows the object keys and values by using the LRU cache. Many methods and APIs which have been used in the following program are explained as follows:

LinkedHashMap:
This is the class of the java.util.*; package. This class is also used for the implementing the doubly linked list which tracks either insertion or access order. The put() method is used for the insertion process to the LinkedHashMap with the value and the unique key regarding the value.

put(Object key, Object value):
This method has been used to add a value with it's unique key in the LRU Cache. This method of the LinkedHashMap class takes two argument in which first is the key and another is the value for the specified key.

Map.Entry:
This interface returns the view of map of collection . The Map.Entry objects are valid only to the duration of the iteration. This is the nested class of the Map class from the java.util.*; package.

e.getKey():
Above method of the Map.Entry class which returns the key corresponding to the value. Here 'e' is the instance of the Map.Entry class.

e.getValue():
Above written is also a method of the Map.Entry class which returns the value corresponding to the key of the index of the LRU Cache.

Here is the code of program:


import java.util.*;

import java.io.*;



public class LRUCacheExample {

  int num = 0;

  LinkedHashMap<String,String> map;

  public static void main (String[] args) throws IOException{

    LRUCacheExample lruCache = new LRUCacheExample();

  }



  public LRUCacheExample() throws IOException{

    System.out.print("Please enter the size of the LRU Cache: ");

    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    try{

      num = Integer.parseInt(in.readLine());

    }

    catch(NumberFormatException ne){

      System.out.println(ne.getMessage() + " is not a legal entry!");

      System.out.println("Please enter a numeric value.");

      System.exit(0);

    }

    map = new LinkedHashMap<String,String>() {

      public boolean removeEldestEntry (Map.Entry<String,String> eldest){

        return size() > num;

      }

    };

    String ch = "N";

    while(!ch.equalsIgnoreCase("Y")){

      System.out.print("Enter key: ");

      String str = in.readLine();

      System.out.print("Enter value: ");

      String str1 = in.readLine();

      map.put (str, str1);

      System.out.print("Do you want to stop the entry(Y/N)?");

      ch = in.readLine();

    }

      

    for (Map.Entry<String,String> e : getAll())

      System.out.println (e.getKey() + " : " + e.getValue());

  }



  public synchronized Collection<Map.Entry<String,String>> getAll() {

    return new ArrayList<Map.Entry<String,String>>(map.entrySet());

  }

}