✨ feat: add LRU cache using map interface #4

Author: pnguyen215

Diff for: docs/001_LRUCache4j.md

@@ -0,0 +1,104 @@
+# LRUCache4j
+
+`LRUCache4j` is a thread-safe implementation of a Least Recently Used (LRU) cache in Java. This class extends the Map
+interface and provides a cache mechanism that evicts the least recently used items when a specified capacity is reached.
+The class ensures thread safety by using a ReentrantReadWriteLock around its read and write operations.
+
+## Features
+
+- **Thread-safe**: Uses ReentrantReadWriteLock to manage concurrent access.
+- **Eviction policy**: Removes the least recently used item when the cache exceeds its capacity.
+- **Implements Map interface**: Can be used as a drop-in replacement for a Map with LRU eviction.
+- **Customizable capacity**: Initialize with a specified capacity to control the maximum number of entries.
+
+## Usage
+
+### Initialization
+
+To create an instance of `LRUCache4j`, simply specify the maximum number of entries it can hold:
+
+```java
+LRUCache4j<String, Integer> cache = new LRUCache4j<>(5);
+```
+
+### Basic Operations
+
+- Put an entry:
+
+```java
+cache.put("key1",1);
+```
+
+- Get an entry:
+
+```java
+Integer value = cache.get("key1");
+```
+
+- Remove an entry:
+
+```java
+cache.remove("key1");
+```
+
+- Check if the cache contains a key or value:
+
+```java
+boolean containsKey = cache.containsKey("key1");
+boolean containsValue = cache.containsValue(1);
+```
+
+- Clear the cache:
+
+```java
+cache.clear();
+```
+
+### Advanced Operations
+
+- Put if absent:
+
+```java
+cache.putIfAbsent("key2",2);
+```
+
+- Bulk operations:
+
+```java
+Map<String, Integer> map = new HashMap<>();
+map.
+
+put("key3",3);
+map.
+
+put("key4",4);
+cache.
+
+putAll(map);
+```
+
+## Thread Safety
+
+`LRUCache4j` uses read-write locks to ensure thread-safe operations. The `readOperation` and `writeOperation` methods
+encapsulate the lock management for read and write operations respectively.
+
+## Example
+
+```java
+public class Example {
+    public static void main(String[] args) {
+        LRUCache4j<String, String> cache = new LRUCache4j<>(3);
+        cache.put("a", "apple");
+        cache.put("b", "banana");
+        cache.put("c", "cherry");
+
+        System.out.println("Cache size: " + cache.size()); // Output: 3
+
+        cache.get("a"); // Access "a" to make it recently used
+        cache.put("d", "date"); // This will evict "b" as it is the least recently used
+
+        System.out.println("Cache contains 'b': " + cache.containsKey("b")); // Output: false
+        System.out.println("Cache contains 'a': " + cache.containsKey("a")); // Output: true
+    }
+}
+```