Java - Default Initialization of static variables before Static initialization [duplicate]

Question

I want to know that does default initialization of static variables happens before static initialization or along with it ?

Let us look at code below:

class Test {

    static {
        System.out.println(Test.a);  // prints 0
        a = 99; // a get 99
        System.out.println(Test.a); // prints 99
    }

    static int a = 10;

    static {
        System.out.println(a); // prints 10
    }

    public static void main(String[] args) {

    }
}

My guess is that when class is loaded , all the static variables are created in memory and default values given to them then and there only. Then static initialization takes place in the order static initializers and static fields that appear in code . Am I right ?

EDIT : I am aware of the order of static initialization but I am unable to get the point in JLS where it tells us that default initialization happens before static initialization takes place ?

Yes. You are right.

cpp beginner
– cpp beginner

2018-03-28 20:15:49 +00:00
Commented Mar 28, 2018 at 20:15 — cpp beginner
– cpp beginner, Commented Mar 28, 2018 at 20:15
stackoverflow.com/questions/10035890/…

Ivan
– Ivan

2018-03-28 20:18:02 +00:00
Commented Mar 28, 2018 at 20:18 — Ivan
– Ivan, Commented Mar 28, 2018 at 20:18

davidxxx · Accepted Answer · 2018-03-28 20:22:28Z

3

You are right.

Static fields and initializers are indeed executed in their declared order :

12.4.2. Detailed Initialization Procedure

Next, execute either the class variable initializers and static initializers of the class, or the field initializers of the interface, in textual order, as though they were a single block.

And at runtime each class variable is indeed initialized with a default value :

4.12.5. Initial Values of Variables

...

Each class variable, instance variable, or array component is initialized with a default value when it is created (§15.9, §15.10):

For type byte, the default value is zero, that is, the value of (byte)0.

For type short, the default value is zero, that is, the value of (short)0.

For type int, the default value is zero, that is, 0. ...

That's why the actual behavior :

static {
    System.out.println(Test.a);  // prints 0 -> default value for `int`
    a = 99; // a get 99
    System.out.println(Test.a); // prints 99 -> value after previous statement executed
}

answered Mar 28, 2018 at 20:22

davidxxx

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2 Comments

Number945 Over a year ago

I am aware of the order of static initialization but I am unable to get the point in JLS where it tells us that default initialization happens before static initialization takes place ?

davidxxx Over a year ago

This part implied that : "Each class variable ... is initialized with a default value when it is created"

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