I was talking to Peter von der Ahé today about optimizing startup time. He asked me to guess how many classes the JVM had to load for a simple hello world application written in Java. He also asked me how long such a program would take to run. I didn't know the answers, so he quickly typed it out on a MacBook Pro.

Here's how to see how many classes are loaded:

java -verbose:class Hello

That results in 594 classes:

[Opened /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/classes.jar]
[Loaded java.lang.Object from /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/classes.jar]
[Loaded java.io.Serializable from /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/classes.jar]
[Loaded java.lang.Comparable from /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/classes.jar]
...
[Loaded java.util.Collections$UnmodifiableMap from /System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Classes/classes.ja

Java takes roughly 0.2 seconds to run hello world:

time java Hello
Hello, World!

real 0m0.212s
user 0m0.221s
sys 0m0.051s

Kind of interesting. I know that this is the world's stupidest benchmark, but I decided to write the same thing in Python. It takes 0.04 seconds.

Dart currently takes 0.02 seconds.

Ruby 1.8.7 takes 0.009 seconds.

C takes 0.006 seconds.

(Warning: bad joke coming...)

Of course, the real reason C is so fast is because it doesn't have any class.