C# Java HashMap equivalent

In Java, the HashMap class is the equivalent of the Dictionary class in C#. It is a map data structure that stores (key, value) pairs and provides fast lookup and insertion of elements.

Here's an example of how you can use a HashMap in Java:

import java.util.HashMap;

HashMap<String, Integer> map = new HashMap<>();

// Add some elements to the map
map.put("Alice", 42);
map.put("Bob", 23);
map.put("Eve", 56);

// Look up an element by key
int age = map.get("Alice");
System.out.println(age); // 42

// Check if the map contains a key
boolean containsKey = map.containsKey("Charlie");
System.out.println(containsKey); // false

// Get the size of the map
int size = map.size();
System.out.println(size); // 3

The HashMap class is part of the java.util package, and it is not synchronized, so it is not thread-safe. If you need a thread-safe map, you can use the ConcurrentHashMap class from the java.util.concurrent package.

import java.util.concurrent.ConcurrentHashMap;

ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();

The ConcurrentHashMap class provides thread-safe access to the map, but it may be slightly slower than the HashMap class.