Question

here is the code

public class ClassResolution {
static class Parent {
    public static String name;
    static {
        System.out.println("this is Parent");
        name = "Parent";
    }

}

static class Child extends Parent {
    static {
        System.out.println("this is Child");
        name = "Child";
    }

}

public static void main(String[] args) throws ClassNotFoundException {
    System.out.println(Child.name);
}}

what ouput i expect is:

this is Parent
this is Child
Child

but actually is:

this is Parent
Parent

it seems static block in Child class does not get executed, but why? it’s anti-intuition, doesn’t it?

supplement：
to make it more clear, i list the 2 1 points below:

1. As @axtavt say, according to JLS 12.4.1, class Child is loaded, but not initialized.
2. But @Alexei Kaigorodov pointed out, according to jvms-5.5,
   class Child should be initialized, because of the execution of
   instruction getstatic on Child class.

what do you think?

supplement2：
@Alexei Kaigorodov has renewed his mind, so it seems no disagreement left. But I think the point of Alexei Kaigorodov is enlightening, so I left it there.

Thank you, everyone.

Answer 1

From JLS 12.4.1:

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, and an assert statement (§14.10) lexically nested within T is executed.

As you can see, nothing of these happens in your code (note that name is declared in Parent, not in Child), therefore Child doesn’t get initialized and its static block doesn’t get executed.

If you do something to trigger initialization of Child, you’ll get an expected output:

new Child();
System.out.println(Child.name); 

Note, however, that static fields are not inherited, therefore Child.name and Parent.name actually refer to the same field. That’s why it doesn’t make much sense to use code similar to your example in practice.

Also note that despite the fact that Child.name actually refers to Parent.name, it’s still referenced as Child.name in the bytecode, therefore your code triggers loading of Child, but not its initialization.