Will the jit optimize new objects

Question

I created this class for being immutable and having a fluent API:

public final class Message {
    public final String email;
    public final String escalat         


        

Answer 1

will the optimizer be able to avoid lots of object creation

No, but instantiation is a very cheap operation on the JVM. Worrying about this performance loss would be a typical example of premature optimization.

Is there anything to be gained from making a separate mutable builder object instead?

Working with immutables is generally a good approach. On the other hand builders also won't hurt you, if you use the builder instances in a small context, so their mutable state is accessible only in a small, local envorironment. I don't see any severe disadvantages on any side, it is really up to your preference.