12. Usage of Static block

Unlike C++, Java supports a special block, called static block (also called static clause) which can be used for static initializations of a class. This code inside static block is executed only once: the first time you make an object of that class or the first time you access a static member of that class (even if you never make an object of that class). For example, check output of following Java program.

Example : 1

// filename: Main.java class Test {     static int i;     int j;           // start of static block     static {         i = 10;         System.out.println("static block called ");     }     // end of static block } class Main {     public static void main(String args[]) {         // Although we don't have an object of Test, static block is         // called because i is being accessed in following statement.         System.out.println(Test.i);     } }

Output:
static block called
10

Also, static blocks are executed before constructors. For example, check output of following Java program.

Example :

// filename: Main.java class Test {     static int i;     int j;     static {         i = 10;         System.out.println("static block called ");     }     Test(){         System.out.println("Constructor called");     } } class Main {     public static void main(String args[]) {        // Although we have two objects, static block is executed only once.        Test t1 = new Test();        Test t2 = new Test();     } }

Output:
static block called
Constructor called
Constructor called