Can you explain how null keys work in Java collections?

Can you explain how null keys work in Java collections?

In Java, some collections like HashMap allow null keys, while others like TreeMap do not. Would you like to know more about specific collections?

What happens if I try to add a null key to a TreeMap?

If you try to add a null key to a TreeMap, it will throw a NullPointerException because TreeMap uses natural ordering or a comparator that cannot handle null.

Are there any collections that allow multiple null keys?

Yes, collections like HashMap and HashSet can have multiple null keys, as they do not impose any restrictions on the number of nulls.

Can you give an example of using null keys in a HashMap?

Sure! In a HashMap, you can do something like this: HashMap<String, String> map = new HashMap<>(); map.put(null, "value"); This will successfully store a null key.