Java Reflection: Why is it so slow?

Question

I\'ve always avoided Java reflection soley based on its reputation for slowness. I reached a point in the design of my current project where being able to use it would make

Answer 1

It seems that if you make the constructor accessible, it will execute much faster. Now it's only about 10-20 times slower than the other version.

    Constructor c = B.class.getDeclaredConstructor();
    c.setAccessible(true);
    for (int i = 0; i < numTrials; i++) {
        c.newInstance();
    }

Normal instaniation took: 47ms
Reflecting instantiation took:718ms

And if you use the Server VM, it is able to optimize it more, so that it's only 3-4 times slower. This is quite typical performance. The article that Geo linked is a good read.

Normal instaniation took: 47ms
Reflecting instantiation took:140ms

But if you enable scalar replacement with -XX:+DoEscapeAnalysis then the JVM is able to optimize the regular instantiation away (it will be 0-15ms) but the reflective instantiation stays the same.