Question

I am unable to understand the following text… Does it mean that <clinit> is for empty constructors? Why is important to have two different versions?

https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-2.html

2.9. Special Methods

At the level of the Java virtual machine, every constructor (§2.12) appears as an instance initialization method that has the
special name <init>. This name is supplied by a compiler. Because the
name <init> is not a valid identifier, it cannot be used directly in a
program written in the Java programming language. Instance
initialization methods may be invoked only within the Java virtual
machine by the invokespecial instruction, and they may be invoked only
on uninitialized class instances. An instance initialization method
takes on the access permissions (§2.7.4) of the constructor from which
it was derived.

A class or interface has at most one class or interface initialization method and is initialized (§2.17.4) by invoking that
method. The initialization method of a class or interface is static
and takes no arguments. It has the special name <clinit>. This name is
supplied by a compiler. Because the name <clinit> is not a valid
identifier, it cannot be used directly in a program written in the
Java programming language. Class and interface initialization methods
are invoked implicitly by the Java virtual machine; they are never
invoked directly from any Java virtual machine inw2struction, but are
invoked only indirectly as part of the class initialization process.

Answer 1

<init> is the (or one of the) constructor(s) for the instance, and non-static field initialization.

<clinit> are the static initialization blocks for the class, and static field initialization.

class X {

   static Log log = LogFactory.getLog(); // <clinit>

   private int x = 1;   // <init>

   X(){
      // <init>
   }

   static {
      // <clinit>
   }

}