builder for HashMap

Question

Guava provides us with great factory methods for Java types, such as Maps.newHashMap().

But are there also builders for java Maps?

HashM         


        

Answer 1

Since Java 9 Map interface contains:

• Map.of(k1,v1, k2,v2, ..)
• Map.ofEntries(Map.entry(k1,v1), Map.entry(k2,v2), ..).

Limitations of those factory methods are that they:

• can't hold nulls as keys and/or values (if you need to store nulls take a look at other answers)
• produce immutable maps

If we need mutable map (like HashMap) we can use its copy-constructor and let it copy content of map created via Map.of(..)

Map map = new HashMap<>( Map.of(1,"a", 2,"b", 3,"c") );