Java Programming

I have a small understanding problem in java.
First a small sample cod

public class Foo {
    private static final String test = "abc";
    static{
            //some code to do certain task
           //when does the code here get executed
     }
}

In the above code, when will the block of code inside the static { block will be executed.
Is it a type of constructor or something else?
Thanx in advance for your ideas in clearing my obstacle.