When are initializer blocks used in java?

Question

I read that an initializer block is "an unnamed code block that contains th code that initializes the class?

For example :

class A {
  final int x;
  final int y;
  final String n;

{ 
    x = 10;
    y = 20;
}

public A(String name ) {

/* etc... etc */

I have never seen this type of code used, so I was wondering where it may be helpful. Why don't we just initialize variables in constructor ?

thanks

Answer 1

A common use for this is the static initializer block:

class A {
    static boolean verbose;
    final int x;
    final int y;
    final String n;

static { 
    verbose = doSomethingToGetThisValue();
}

public A(String name ) {

/* etc... etc */

This is useful because your static variables might be used by a static method before an instance of the class is ever created (and therefore before your constructor is ever called).

See also this SO answer.