Static block vs static method - initializing static fields

Question

Out of curiosity, I measured the performance between static block and static method initializer. First, I implemented the above mentioned methods in two separate java classes, like so:

First:

class Dummy {
    static java.util.List<Integer> lista = new java.util.ArrayList<Integer>();
    static {
        for(int i=0; i < 1000000; ++i) {
            lista.add(new Integer(i));
        }
    }
}

public class First {
    public static void main(String[] args) { 
        long st = System.currentTimeMillis();
            Dummy d = new Dummy();
        long end = System.currentTimeMillis() - st;
        System.out.println(end);    
    }
}

Second:

class Muddy {
    static java.util.List<Integer> lista = new java.util.ArrayList<Integer>();
    public static void initList() {
        for(int i=0; i < 1000000; ++i) {
            lista.add(new Integer(i));
        }
    }
}

public class Second {
    public static void main(String[] args) { 
        long st = System.currentTimeMillis();
            Muddy.initList();
            Muddy m = new Muddy();
        long end = System.currentTimeMillis() - st;
        System.out.println(end);    
    }
}

Then I executed this little batch script to measure it 100 times and put the values in a file. batchFile.bat First Second dum.res.txt

After that, I wrote this piece of code to calculate mean value and standard deviation of Dummy's and Muddy's measured values.

This is the result that I've got:

First size: 100 Second size: 100
First       Sum: 132    Std. deviation: 13
Second      Sum: 112    Std. deviation: 9

And it is similar on my other machines...every time I test it.

Now I'm wondering, why is it so? I checked the bytecode and Second.class has one instruction more (call to static initList()) between calls to System.currentTimeMillis(). They both do the same thing, but why is the First one slower? I can't really reason it out just by looking at the bytecode, since this was my first time touching javap; I don't understand bytecode yet.

Answer 1

I think that the reason why the static block version is slower than the static method version could be due to the different JIT optimization that they get ...

See this interesting article for more interesting information : Java Secret: Are static blocks interpreted?