Static nonstatic class object constructor

Question

I was wonderring what is the use of non static constructors??
we all know about static constructors, they are used for initializing the class.
we all know about constructos, they are used for initializing an object from a given class.
what I dont know is the use of non static constructors such as this
class A{
     static{
          System.out.println ("Class A Static Constructor");
          /*What is the use of this???????
           *why dont we put this inside the constructor??
          System.out.println ("Class A NON static constructor");
     A(){
          System.out.println ("Class A Constructor");
class B extends A{
     static{
          System.out.println ("Class B static constructor");
          System.out.println ("Class B NON static Constructor");
     B(){
          System.out.println ("Class B Constructor");
public class Test{
     public static void main(String[]args){
          new B();
          new B();
}I would appreciate understaind this!! I can only see that if there was no other constructor, it can be used instead of the default constructor() with no arguments,
any clarification?

Answer 1

They are called static and non static intializer.
The non static initializer was introduced in the language subsequently with inner classes.
It's used the give an anonymous inner class a feature that behaves like a constructor (though with no args).
It's useless for other kinds of class.
abstract class A{
     A(){
          System.out.println("A constructor");
     abstract void exec();
class B{
     static A getA(){
          return new A(){
                         System.out.println("the cool implementation");
                    void exec(){
                         System.out.println("exec()");
     public static void main( String[] args){
          A a = B.getA();
          a.exec();
}Cut and paste in a new text file, call it B.java, then javac B.java, and java B.