LRUCacheImplementation

LRUCache

import java.util.HashMap;
import java.util.Map;

public class LRUCache {

	private static class Database {
		private Map<Integer, Integer> map = new HashMap<Integer, Integer>() {
			{
				put(1, 1);
				put(2, 2);
				put(3, 3);
				put(4, 4);
				put(5, 5);
			}
		};

		public int read(int key) {
			return map.get(key);
		}

	}

	private static class Entry {
		int value;
		Entry succ;
		Entry prev;

		public Entry() {

		}

		public Entry(int value) {
			this.value = value;
		}

		public void addFirst(Entry temp) {
			this.succ.prev = temp;
			temp.prev = this;
			temp.succ = this.succ;
			this.succ = temp;
		}

		public void removeLast() {
			Entry.remove(this.prev);
		}

		public static void remove(Entry temp) {
			temp.prev.succ = temp.succ; // delete node
			temp.prev.succ.prev = temp.prev;
		}

		public void print() {
			Entry index = this.succ;
			while (index != this) {
				System.out.print(index.value + " ");
				index = index.succ;
			}
			System.out.println();
		}

		public static Entry newInstance() {
			Entry temp = new Entry();
			temp.prev = temp;
			temp.succ = temp;
			return temp;
		}
	}

	Database database;
	int size;
	int currentFill;
	HashMap<Integer, Entry> map;
	Entry list;

	public LRUCache(Database database, int size) {
		this.database = database;
		this.size = size;
		map = new HashMap<Integer, Entry>();
		list = Entry.newInstance();
	}

	public int get(int key) {
		Entry temp = map.get(key);
		if (null == temp) {
			put(key, database.read(key));
		}else{
			Entry.remove(temp);
			list.addFirst(temp);
		}
		//list.print();
		return map.get(key).value;
	}

	public void put(int key, int value) {
		Entry temp = map.get(key);
		if (null == temp) {
			temp = new Entry(value);
			if (size == currentFill) {
				list.removeLast();
				currentFill--;
			}
			map.put(key, temp);
			currentFill++;
		} else {
			temp.value = value;// update value
			Entry.remove(temp);
		}
		list.addFirst(temp);
		//list.print();
	}

	public static void main(String[] args) {
		Database database = new Database();
		LRUCache cache = new LRUCache(database, 3);
		for (int i = 1; i <= 5; i++) {
			cache.get(i);
		}
		cache.get(4);  
		cache.get(4);
		cache.put(5,5);
	}
}