Java Reflection Performance

Question

Does creating an object using reflection rather than calling the class constructor result in any significant performance differences?

Answer 1

If there really is need for something faster than reflection, and it's not just a premature optimization, then bytecode generation with ASM or a higher level library is an option. Generating the bytecode the first time is slower than just using reflection, but once the bytecode has been generated, it is as fast as normal Java code and will be optimized by the JIT compiler.

Some examples of applications which use code generation:

• Invoking methods on proxies generated by CGLIB is slightly faster than Java's dynamic proxies, because CGLIB generates bytecode for its proxies, but dynamic proxies use only reflection (I measured CGLIB to be about 10x faster in method calls, but creating the proxies was slower).

• JSerial generates bytecode for reading/writing the fields of serialized objects, instead of using reflection. There are some benchmarks on JSerial's site.

• I'm not 100% sure (and I don't feel like reading the source now), but I think Guice generates bytecode to do dependency injection. Correct me if I'm wrong.