syntax - Why is this Java code in curly braces ({}) outside of a method?

Question

I am getting ready for a java certification exam and I have seen code LIKE this in one of the practice tests:

class Foo {  
    int x = 1;  
    public static void main(String [] args) {  
        int x = 2;  
        Foo f = new Foo();  
        f.whatever();  
    }  
    { x += x; }  // <-- what's up with this?
    void whatever() {  
        ++x;  
        System.out.println(x);  
    }  
}

My question is ... Is it valid to write code in curly braces outside a method? What are the effects of these (if any)?

Answer 1

Borrowed from here -

Normally, you would put code to initialize an instance variable in a constructor. There are two alternatives to using a constructor to initialize instance variables: initializer blocks and final methods. Initializer blocks for instance variables look just like static initializer blocks, but without the static keyword:

{
    // whatever code is needed for initialization goes here
} 

The Java compiler copies initializer blocks into every constructor. Therefore, this approach can be used to share a block of code between multiple constructors.

You may also wanna look at the discussions here.