Behavior of static blocks with inheritance

inheritance, java, static, static-block

Solution

As I understand. You don't call any `Derived` properties (`myVar` belongs to `Base`, not to `Derived`). And java is not running static block from `Derived`. If you add some static field to `Derived` and access it, then java executes all static blocks.

class Base {

    static public int myVar;

}


class Derived extends Base {

    static public int myVar2;

    static
    {
        Base.myVar = 10;
    }
}


public class Main {
    public static void main( String[] args ) throws Exception {
        System.out.println(Derived.myVar2);
        System.out.println(Base.myVar);
    }
}

From java specification, when class is initialized (and static block got executed):

12.4.1 When Initialization Occurs A class or interface type T will be initialized immediately before the first occurrence of any one of the following:

• T is a class and an instance of T is created. • T is a class and a static method declared by T is invoked. • A static field declared by T is assigned. • A static field declared by T is used and the field is not a constant variable (§4.12.4). • T is a top level class (§7.6), and an assert statement (§14.10) lexically nested within T (§8.1.3) is executed.

Problem

I am trying to use static blocks like this: I have a base class called `Base.java` ``` public class Base { static public int myVar; } ``` And a derived class `Derived.java`: ``` public class Derived extends Base { static { Base.myVar = 10; } } ``` My `main` function is like this: ``` public static void main(String[] args) { System.out.println(Derived.myVar); System.out.println(Base.myVar); } ``` This prints the out put as `0 0` where as I expected `10 0`. Can somebody explain this behavior? Also, if I want my derived classes to set the values for a static variable how can I achieve that?

Original source