What is the difference between HashMap and Hashtable in Java?

Hello colleagues! I started learning the Java Collections Framework and came across two similar classes: HashMap and Hashtable. Both seem to implement the Map interface and store key-value pairs. But I noticed that in modern code everyone uses HashMap, while Hashtable is considered outdated. I wrote a simple example where both classes behave the same: ```java import java.util.*; public class MapTest { public static void main(String[] args) { Map hashMap = new HashMap<>(); hashMap.put("key1", "value1"); hashMap.put(null, "nullValue"); System.out.println("HashMap: " + hashMap.get("key1")); Hashtable hashtable = new Hashtable<>(); hashtable.put("key1", "value1"); // hashtable.put(null, "nullValue