How to implement cache in java using hashmap without

How to implement cache in java using hashmap without

Implementing a cache in Java using a HashMap without third-party libraries involves creating a custom cache class that leverages the benefits of Hash Maps to store and retrieve cached data efficiently.

Here's an example implementation:

import java.util.HashMap;
import java.util.Map;
public class Cache<K, V> {
private Map<K, V> cacheMap = new HashMap<>();
private int cacheSize; // maximum size of the cache
public Cache(int capacity) {
cacheSize = capacity;
}
public void put(K key, V value) {
if (cacheMap.size() >= cacheSize) {
// evict the least recently used item from the cache
K evictKey = getEvictionKey();
cacheMap.remove(evictKey);
}
cacheMap.put(key, value);
}
public V get(K key) {
return cacheMap.getOrDefault(key, null); // return null if not found in cache
}
private K getEvictionKey() {
// implement an eviction policy (e.g., LRU, FIFO)
// for this example, we'll use a simple FIFO approach
K[] keys = (K[]) cacheMap.keySet().toArray(new K[0]);
return keys[0]; // evict the first item in the list
}
public void clear() {
cacheMap.clear();
}
}

In this implementation:

This implementation demonstrates a basic LRU eviction policy. You can modify or extend this code to implement more sophisticated policies (e.g., LFU, Random) depending on your specific use case and performance requirements.

Here's how you could use this Cache class:

public class Example {
public static void main(String[] args) {
Cache<String, Integer> cache = new Cache<>(10); // 10-slot cache
cache.put("key1", 10);
cache.put("key2", 20);
cache.put("key3", 30);
System.out.println(cache.get("key1")); // prints 10
System.out.println(cache.get("key4")); // prints null (not found in cache)
cache.clear(); // clears the entire cache
cache.put("newKey", 40); // adds a new item to the cleared cache
}
}

This example demonstrates basic usage of the Cache class. You can modify it to fit your specific requirements and test its performance and functionality.

Remember that this is just a simplified implementation, and you should consider factors like concurrency, thread safety, and cache expiration when designing a production-ready cache system.

How does HashMap implemented in Java?

HashMap is a fundamental data structure in the Java programming language that provides an efficient way to store and retrieve key-value pairs. The implementation of HashMap in Java is based on the concept of hashing, which maps keys to indices of an array.

How Does HashMap Work?

A HashMap in Java consists of a collection of key-value pairs, where each pair is represented by a key and its corresponding value. The key is used as an index into a backing array, which stores the actual values. Here's a high-level overview of how HashMap works:

HashMap Implementation

The HashMap class in Java is implemented as an abstract data type that provides methods for adding, removing, and retrieving key-value pairs. The implementation is based on the following components:

The implementation of HashMap in Java involves several optimizations and tweaks to ensure efficiency and performance:

Performance Considerations

To achieve optimal performance, the Java implementation of HashMap has several performance considerations:

In summary, the HashMap implementation in Java provides an efficient way to store and retrieve key-value pairs by leveraging hashing, collision resolution through chaining, and dynamic resizing. The optimizations and tweaks made to the implementation ensure that it remains performant and scalable for a wide range of applications.