Java static Block: Definition and Usage

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.

Program

// filename: MainClass.java
class Test {
    static int i;
    int j;

    // start of static block
    static {
        i = 20;
        System.out.println("static block called ");
    }
    // end of static block
}

class MainClass {
    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:

show method of sub class.
display method of super class.
Press any key to continue . . .

static blocks are executed before constructors.

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

Program

// filename: MainClass.java
class Test {
    static int i;
    int j;

    // start of static block
    static {
        i = 20;
        System.out.println("static block called ");
    }
    // end of static block
}

class MainClass {
    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:

show method of sub class.
display method of super class.
Press any key to continue . . .