Can I remove any implicitly imported Java library?

Question

Can I remove any implicitly imported Java library? It may not seem useful. But I think it may reduce some execution time!

Answer 1

This will have no effect on execution type - I think I'm correct in saying that, by default, classes are only loaded as and when they are needed, not on mass at start-up.

To improve performance you need to profile your application with a tool like Visual VM and address the bottlenecks it identifies (which will never be where you'd expect).

Answer 2

Imports are just syntactic sugar. All they do is let you access things in other packages without having to state their fully qualified name. The code that is produced is exactly the same as if you fully-qualified everything. So there is no runtime performance penalty to having imports.

This also goes for the "implicit imports" (ie: java.lang): you don't pay any price for the classes you don't actually use.

Answer 3

Java doesn't include all of the classes in java.lang.* in your program. The compiler only includes the ones you explicitly use (or are used by classes you use, etc.).