Overview
This document will outline when to use Guava's ImmutableMap/ImmutableSet and Java's Map.of and Set.of.
(Maps and Sets are similar to how they work (in terms of them being Unmodifiable and Immutable). This document will use maps as an example but the theory is the same for both)
Background
Unmodifiable vs Immutable
In Java there are unmodifiable maps. These are maps which are wrappers over a modifiable map. With these, if a change is made on the modifiable map then it is reflected in the unmodifiable map.
Map<String, String> mutableMap = new HashMap<>(); Map<String, String> unmodifiableMap = Collections.unmodifiableMap(mutableMap);
Guava's ImmutableMap, on the other hand, contains its own private data and doesn't allow modification to it. Therefore, the data cannot change in any way once an instance of the Immutable Map is created.
ImmutableMap<String, String> immutableMap = ImmutableMap.copyOf(mutableMap);
Map.of/Set.of
In Java 9, Map.of and Set.of were introduced. These are static factory methods which took values on the fly and returned Unmodifiable maps/sets which contained those values.
Map<String, String> immutableMap = Map.of("A", "Apple", "B", "Ball", "C", "Car")
Guava also has an ImmutableMap.of/ImmutableSet.of and they work in the same way Java's Map.of/Set.of work.
Implementation
Comments on Unmodifiable vs Immutable
If you want Immutable Map/Set then use Guava's ImmutableMap/ImmutableSet. As Java's Unmodifiable Map/Set are not truly immutable.
When to use Map.of/Set.of
To avoid any sonarcloud complains, use Map.of/Set.of when you want to create an Immutable map/set on the fly. Even though an unmodifiable map/set is returned, this is still an immutable map/set as there is no mutable map/set that can be changed.