Classes should be immutable unless there’s a very good reason to make them mutable. ... Several resources outline the steps necessary to write a Java class that will lead to immutable Java objects.

Java could gain a capability for sharing immutable data across threads, based on a plan now under consideration in the OpenJDK realm. An OpenJDK proposal for extent-local variables, currently an ...

But, there is another approach called immutable Linux, and it's been gaining popularity over the last few years. Immutable Linux distributions come with a read-only core system.