Collections.unmodifiable map 的替代品是什么，可以同时访问不可修改的 Map

Question

With the deprecation of edu.emory.mathcs.backport.java.util.Collections.unmodifiableMap , what is the alternative for concurrent access to UnmodifiableMaps?

Answer 1

You don't need to protect an UnmodifiableMap (or any immutable object for that matter) against concurrent access.

That's the whole point of immutability.

Answer 2

Collections.unmodifiableMap returns a view onto original map, not a copy

java.util.Collections.unmodifiableMap is not deprecated.

As for concurrent access to the map, you have no issue if using the refeference returned by this method. But beware: the returned reference is a view nack onto the original map. So if the original map is changing while you are utilizing the unmodifiable view, you will have concurrency problems.

Map.copyOf

I suggest instead that in Java 10 and later you instead call Map.copyOf . This method makes an actual copy of the map rather than a view. So the result is unrelated to the original. Adding or removing entries in the original map has no effect on the non-modifiable map returned by this method.

Map< DayOfWeek , Person > map = new HashMap<>() ;
…
Map< DayOfWeek , Person > mapUnmod = Map.copyOf( fix