When will we go for static block...?

[Naveen Raja]

Hi,

I know that static block can be defined in a class,but when we have to go for it and how compiler treats it..?

Thanks in Advance

Naveen.

[Nikhil Goel]

static blocks are intialized the first thing even way before constructors.

Usage can be to intialize connection pools etc . Normall all other utility stuff can be taken care in static blocks

[Ilja Preuss]

JDBC driver, for example, use static blocks to register themselves to the DriverManager. That's why loading a JDBC driver by Class.forName initializes it.

Another use is to initialize complex static variables, such as Collections etc.

They shouldn't be used too often, though - most often there are better (more flexible) alternatives to static blocks.

[Sol Mayer-Orn]

Just wanted to add that a static block is executed when the class is first loaded & initialized for use.
The JVM spec has more accurate definitions about this, but usually you'll notice that a class is loaded & initialized when you first use it - e.g. when you first try to create an instance, or use some static methods/variables.

A classic example:

    // Class with a static initializer:
    public class MyClass {
         static {
               System.out.println("running static block");
         }
         public MyClass(){
         }    
    } 
 
    // Usage:
    public class Main {
         public static void main(String[] args) throws Exception{
               MyClass instance=null;  // MyClass is not loaded yet !
               int x= 4+4;             // MyClass is not loaded yet!
               Thread.sleep(10000);    // waiting... MyClass is not loaded yet
               instance=new MyClass(); // first usage - static initializer will run!
               MyClass instance2=new MyClass(); // static initializer will NOT run again    
 
         }
    }
 

[Pratibha Malhotra]

To add to Naveen Question, what all resolutions happen at compile time and what all are left for run time.

can someone pls point me to appropriate resource

thanks ahead,