Class Loading time in Java

Question

Hi stackoverflow members, Here is a little question related to the actual meaning of "class loading time".

For example the following code:

public class Sequence {
    Sequence() {
        System.out.print("c ");
    }
    {
        System.out.print("y ");
    }
    public static void main(String[] args) {
        System.out.println("Indeed");
        new Sequence().go();
    }
    void go() {
        System.out.print("g ");
    }
    static { System.out.println("x "); }
} 

It does print out first "x" which is static so the static init blocks are always loaded at "class loading time". I get it, but do you know exactly when this loading time happens? I thought when the class first gets called in the main method by creating the first object but in that case the result should have been different by printing out first "Indeed". Anyone can help me clarifying this doubt? I have checked other post talking about this argument in general but still I think would be much clearer (at least for me) getting to know when exactly, in the code reported above, the "class loading time" happens.

Thanks in advance.

Answer 1

The answer to your question is in the JLS Chapter 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.

I recommend you start reading a few lines above at JLS Chapter 12.4. Initialization of Classes and Interfaces

Just start with Chapter 12. Execution, it exactly describes when a class needs to be loaded. The initialization will be done after loading it.