Who invokes the class initializer method <clinit> and when?

Question

I know that the new, dup, invokespecial and astore bytecode pattern will invoke the instance initializer method <init> when someone instance a Java class from the Java language point of view, but i never figure out who invoke the special <clinit>method and when does this happen?

My guess is that <clinit> is invoked before <init> method. Can any body give me some information to prove it? Is this documented in the JVM Specification or Java Language Specification?

Answer 1

<clinit> is a static method added by javac and called by JVM after class loading. We can see this method in class bytecode with bytecode outline tools. Note that <clinit> is added only if a class needs static initilization, e.g

public class Test1 {
    static int x  = 1; 

    public static void main(String[] args) throws Exception {
    }
}

public class Test2 {
    static final int x  = 1; 

    public static void main(String[] args) throws Exception {
    }
}

Test1 has <clinit> because its field x needs to be initialized with 1; while Test2 has no <clinit> method because its x is a constant.

It's also interesting to note that Class.forName has boolen intialize param which determines if the class should be initialized after loading or not.