Why does Map.of not allow null keys and values?

Question

With Java 9, new factory methods have been introduced for the List, Set and Map interfaces. These methods allow quickly instantiating a Ma

Answer 1

While HashMap does allow null values, Map.of does not use a HashMap and throws an exception if one is used either as key or value, as documented:

The Map.of() and Map.ofEntries() static factory methods provide a convenient way to create immutable maps. The Map instances created by these methods have the following characteristics:

• ...

• They disallow null keys and values. Attempts to create them with null keys or values result in NullPointerException.