Help required in understanding of static blocks in java

Question

Hi ,
Can some one help me in understanding the difference between static blocks in java....also what is the difference in declaring some static variables in a class and and declaring some variables in a static block? From an architecture viewpoint when should one use static blocks in Java?

Answer 1

Static blocks are piece of code that can beexecuted
before creating an instance of a class.static blocks are executed once, when the class
itself is loaded by the JVM. They are not executed
before creating each instance of a class.
For example whatever you include in the mainn method will be
executed without you having to create the instanceof
the class using the new operator. So you can saythe
main method is a static block.main is not a static initialisation block but a
static method. a special case static method at that -
it is only executed when the containing class is
specified as a parameter to the JVM. (unless you
specifcally call it elsewhere in code - but that
would be bad form).
in answer to the original post, static variables
belong to the class. each instance of the class share
the same static variables. Public static vars can be
accessed by prefixing them with the class name. A
static initialisation block can be used to
initialise static variables. Variables declared
within the static initialisation block exist only
within the scope of the block.
e.g.
public class Foo {
static Bar bar;        // static member variable
// static initialisation block
static {
// variable declared in static block...
String barInfo =
arInfo = System.getParameter("barInfo");
// ... used to initialise the static var
bar = new Bar(barInfo);
So is the only purpose of static initialization blocks is to initialize static variables? Does the initialization of static variables inside a static block make any difference in performance? If yes , then how ?