Java initialization order

http://1001javatips.com/initializationorder.htm

The general order of class initialization is:

1 - First all static items are initialized, in their source code order..

2 - Then all member variables are initialized.

3 - Lastly the constructor is called.

  The general order of initialization for classes with inheritance is:

First, parent static items, then child static items

Then parent member variables, followed by the parent constructor

Then child member variables, followed by the child constructor

http://www.thejavageek.com/2013/07/21/initialization-blocks-constructors-and-their-order-of-execution/

• Initialization blocks run in the order they appear in the program.
• Static initialization blocks run when the class is first loaded into JVM
• Instance initialization blocks run whenever a new instance of class is created.

http://www.danielschneller.com/2010/07/java-object-initialization-order-know.html

this shows why it is a bad idea to write theInitializer like this. It should not be aware of Upper's subclasses at all! Instead, if for some reason initialization of certain fields cannot be done in the Lower class itself, it will just require its own variant of some sort of initialization helper. In that case, it would really make no difference if you used String lowerString; or String lowerString = null; - just as it should be.

public class Upper {
 String upperString;

 public Upper() {
  Initializer.initialize(this);
 }
}

package com.ds.test;

public class Lower extends Upper {

 String lowerString = null;

 public Lower() {
  super();
  System.out.println("Upper:  " + upperString);
  System.out.println("Lower:  " + lowerString);
 }

 public static void main(final String[] args) {
  new Lower();
 }
}

package com.ds.test;
public class Initializer {
 static void initialize(final Upper anUpper) {
  if (anUpper instanceof Lower) {
   Lower lower = (Lower) anUpper;
   lower.lowerString = "lowerInited";
  }
  anUpper.upperString = "upperInited";
 }
}

What output is to be expected from running the Lower class?

In this very reduced example it is much easier to get a view of the whole situation - in reality where this occurred there was a lot more code to distract one's attention...
Anyway, this is what the output looks like:

Upper:  upperInited
Lower:  null;

public class Lower extends Upper {

 String lowerString;

 public Lower() {
  super();
  System.out.println("Upper:  " + upperString);
  System.out.println("Lower:  " + lowerString);
 }

 public static void main(final String[] args) {
  new Lower();
 }
}

The output is now:

Upper:  upperInited
Lower:  lowerInited