Why my class is not getting loaded

Question

I am confused with the output of the below code. I know first static block gets executed after class loading but why is my class Test6 not getting loaded. Can someone please clarify.

package com.vikash.General;

public class Test5 {

    public static void main(String[] args) {
        System.out.println(Test6.FOO);
    }
    static {
        System.out.println("Initializing B");
    }
}
class Test6{

    public static final String FOO = "foo";
    static {
        System.out.println("Initializing A");
    }
}

I am getting o/p Initializing B foo – Vikash Mishra May 19 '16 at 09:47 — Vikash Mishra, May 19 '16 at 09:47

score 9 · Answer 1 · edited May 23 '17 at 11:53

9

Test6.FOO refers to Test6, but the field is a public static final String initialized from a compile-time constant, so it will be inlined by the compiler, and Test6 does not need to be loaded at all.

edited May 23 '17 at 11:53

Community

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answered May 19 '16 at 09:53

Thilo

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Indeed. When removing the `final` the static initalizer will be invoked – Clayn May 19 '16 at 09:54
@Thilo Can you explain "it will be inlined by the compiler". I cannot understand. This is new to me – mubeen May 19 '16 at 10:00
1

In effect, the code becomes `System.out.println("foo")`. The compiler replaces the reference to the field with the String literal. At runtime, `Test6` is not needed for this line of code. – Thilo May 19 '16 at 10:01
2

This can lead to problems if you later change `Test6.FOO` to another string. `Test5` will still print the old version (unless you also recompile `Test5`). – Thilo May 19 '16 at 10:02

score 2 · Answer 2 · answered May 19 '16 at 09:53

2

It seems to be because the compiler is inlining the reference to the string literal "foo", so the JRE doesn't actually bother loading Test6 to get it.

If you make a change such as:

public static final String FOO = new String("foo");

then the class Test6 does get loaded (and its static block gets executed).

answered May 19 '16 at 09:53

khelwood

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It also works with a literal when `FOO` is not final. But in case it should be, your solution works as well. – Clayn May 19 '16 at 09:55

score 0 · Answer 3 · answered May 19 '16 at 09:53

0

Use a class loader you will get the desired output

Class.forName("<package>.Test6");

answered May 19 '16 at 09:53

Helios

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Why not just `Class> foo = Test6.class` ? – Thilo May 19 '16 at 09:53
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anything would work. I just gave it as OP was confused about class loading issue. – Helios May 19 '16 at 09:55
Not really. An expression like `System.out.println(Test6.FOO)` would normally also load the class (but not in this case). – Thilo May 19 '16 at 09:57

score -3 · Answer 4 · answered May 19 '16 at 09:54

-3

Test6 is not initialized at all.

the foo is static, which means it can be used before class is intitialized and after a class is load.

answered May 19 '16 at 09:54

sotondolphin

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I don´t know if i understand this answer completly, but i am pretty sure it´s wrong and doesn´t answer the question. – SomeJavaGuy May 19 '16 at 09:58
because it doesn´t explain why `Test6` is not loaded. It is just follwed by a confusing explenation of `foo is static`, which at this point is unrelated to the behavior. Actually this is the question, despite `foo` beeing `static`, why doesn´t it load `Test6` and hence call the `static initializer block` – SomeJavaGuy May 19 '16 at 10:00
I told you it's loaded into JVM but not initialized. – sotondolphin May 19 '16 at 10:01
1

So you are telling foo can be used before class is initialized and after a class load but not in between? I am really confused what you want to tell us and which class do you refer to. – tak3shi May 19 '16 at 10:07

Why my class is not getting loaded

4 Answers4