Custom Cache

This project is a coding test suggested by a java recruiter. The main goal is to create a Cache Manager with a fixed size.

Warning: This code is not thread safe

Usage

Every cache instance must have a size. This size is the number of elements inside the cache container. When the cache is full the oldest element will be evicted. When you add a new value to the registry, the cache manager creates a timestamp to handle the life of the registry.

Every operation over the cache manager should update the timestamp of the accessed object, therefore those not recently accessed could be evicted.

Operations that updates the timestamp are:

put
get
update

So, if you try to add a new value using the "put" method, but the cache is full then automatically the cache manager will evict the oldest value.

coding example

Beware of The code fence below. It shows a coding example with no exception handling.

          int cacheSize = 2;
          Cache<Integer, Integer> cache = new Cache<>(cacheSize);
          cache.put(1, 1);
          cache.put(2, 2); 
          cache.get(1); // returns 1
          cache.put(3, 3); // evicts key 2
          cache.get(2); // returns -1 (not found)
          cache.get(3); // returns 3.
          cache.put(4, 4); // evicts key 1.
          cache.get(1); // returns -1 (not found)
          cache.get(3); // returns 3
          cache.get(4); // returns 4

Create your own Cache Manager instance

Create a Cache Instance defining key type, and the Value type. Assume we want to store links from images, then we'd have the following code snippet:

          int cacheSize = 5;
          Cache<String, String> cache = new Cache<>(cacheSize);

Add new values

          cache.put("img1", "https://picsum.photos/200/300");
          cache.put("placeholder1", "https://picsum.photos/100/100");
          cache.put("placeholder3", "https://picsum.photos/500/200");

Play around with the operations by reading the javadoc.

Background operation

Data representation

Below is the information we need to represent using the cache manager.

k	V	Timestamp
image1	img1.jpg	121212
image2	img2.png	232323
image3	img3.png	121212

Where K is the resource identifier, V is the value represented by K and timestamp is the moment of the operation.

Basically, we need to create a relation among the Key, the value and the timestamp. The idea is simple: Store the key sorted by time and store the value related to key. The relation between K and V is handled by a Hashmap, and it's used a SortedTreeMap to handle the relation between K and timestamp .

Classes

Cache.java : cache manager that handles the key, and the value by using a CacheData instance which is a pojo.
CacheData.java: Pojo to ease the data handling between cache manager and TimeStampLog instance
TimeStampLog.java: Helper class, makes it easy to sort the K by its timestamp.

DanyelMorales / Cache