A static block or a static initializer is a block that
appears within a class definition but outside any member
definition with the keyword static ahead of it. Example:


class MyClass {
    private static double myValue;
    static {
        myValue = Double.parseDouble( System.getProperty(
"version" ) );
    }
}

It is mainly used to perform static construction i.e.
initialization of static variables (see above example). The
static initializer is executed when the class is loaded by
the JVM.

static block contains  a code which is executed without 
object of  a class.i.e is excuted at the time of class 
loading

static block is used to initialization during the JVM start 
up

Static block is executed when the class is loaded into the 
memory before the main(). Only once it will be executed.