Question

Ok so this is a newbie question on java, but i can’t seem to get my head around it.

I have the following code inside my class

private static final String [] LIST_CODE = gerarListCode();
private static final int [][] LIST_INTEGER = new int [][] {
        {947,947}, {110,103}, 
        {947,958}, {110,120}, 
        {947,954}, {103,107}, 
        {947,967}, {110,99,104}};

 private static String [] gerarListCode()
    {
        String [] listCode = new String [LIST_INTEGER.length];

        for (int i=0 ; i<LIST_INTEGER.length ; i++)
        {
           //do some stuff      
        }

        return listaUnicode;
    }

This code is giving me a initialization exception due to a nullpointerexception in the following line

 String [] listCode = new String [LIST_INTEGER.length];

Seems the variable LIST_INTEGER is null at that time.

Can someone explain why? is the classloader process linear, in other words, does it invoke the method before fully loading all the other variables?

Answer 1

Yes, in short, it is linear.

“What the compiler actually does is to
internally produce a single class
initialization routine that combines
all the static variable initializers
and all of the static initializer
blocks of code, in the order that they
appear in the class declaration. This
single initialization procedure is run
automatically, one time only, when the
class is first loaded.”

Taken from Java in a nutshell.

http://www.developer.com/java/other/article.php/2238491

You should define the variables and then initialize them in a static intitializer block in the correct order, or you could swap the order of the statements as follows:

private static final int [][] LIST_INTEGER = new int [][] { {947,947}, {110,103}, 
        {947,958}, {110,120}, 
        {947,954}, {103,107}, 
        {947,967}, {110,99,104}};

private static final String [] LIST_CODE = gerarListCode();