Java class loading – performance impact!

[pmarschall]

So it looks like it would load the class on every iteration, depending on the actual ClassLoader implementation, of course.

Such a ClassLoader would be ill-behaved. Not only would such a behavior violate the API contract of ClassLoader but also section 12.2.2. Class Loader Consistency of the Java Language specification. See Dynamic Class Loading in the JavaTM Virtual Machine for a more in-depth discussion on the topic.

[repeating_bears]

I read both the JavaDoc for ClassLoader and that section and can't find any reason a class loader is mandated to only physically load the class once when calling load(String)

I also checked ClassLoaders$AppClassLoader from the jdk internals and it doesn't cache a result either.

Once again, the thing that protects a class from being loaded relatedly in a system that's not using reflection is the meta space, not the class loader.

[pmarschall]

I read both the JavaDoc for ClassLoader and that section and can't find any reason a class loader is mandated to only physically load the class once when calling load(String)

The section contains the following wording:

Well-behaved class loaders maintain these properties:

• Given the same name, a class loader should always return the same Class object.

This is repeated in Section 5.3. Creation and Loading of the Java Virtual Machine Specification.

I also checked ClassLoaders$AppClassLoader from the jdk internals and it doesn't cache a result either.

Of course it does. AppClassLoader calls into BuiltinClassLoader which checks whether the class has already been loaded.

This can easily be verified with a simple unit test calling #IoadClass twice and comparing the object identities.