Java reflection run-time performance

Question

This is an academical exercise (disclaimer).

I'm building an application that will profit from being as fast as possible as it will compete with others.

I know that declaring a class using reflection (example below) will suffer a huge penalty as opposed to a standard declaration.

Class mDefinition = Class.forName("MySpecialClassString");
Constructor mConstructor = mDefinition.getConstructor(new Class[]{MySpecialClass.class});
myClass = (MySpecialClass) mConstructor.newInstance(this);

However, after declaring myClass if I use it in a standard fashion myClass.myMethod() will I also suffer from performance hogs or will it be the same as if I had declared the class in a standard fashion?

Answer 1

There will be a performance penalty when you first instantiate the object. Once the class is loaded, its the same as if it had been instantiated normally, and there will be no further performance penalty.

Going further, if you call methods using reflection, there will be a performance penalty for about fifteen times (default in Java), after which the reflected call will be rewritten by the JVM to be the exact same as a statically compiled call. Therefore, even repeatedly reflected method calls will not cause a performance decrease, once that bytecode has been recompiled by the JVM.

See these two link for more information on that:

• Any way to further optimize Java reflective method invocation?
• http://inferretuation.blogspot.com/2008/11/in-jit-we-trust.html