When and where static blocks are executed in java?

A static block is a block of code with a static keyword. In general, these are used to initialize the static members. JVM executes static blocks before the main method at the time of class loading.

Example

 Live Demo

public class MyClass {
   static{
      System.out.println("Hello this is a static block");
   }
   public static void main(String args[]){
      System.out.println("This is main method");
   }
}

Output

Hello this is a static block
This is main method

Executing a static block

JVM first looks for the main method (at least the latest versions) and then, starts executing the program including static block. Therefore, you cannot execute a static block without main method.

Example

 Live Demo

public class Sample {
   static {
      System.out.println("Hello how are you");
   }
}

Since the above program doesn’t have a main method, if you compile and execute it you will get an error message.

C:\Sample>javac StaticBlockExample.java
C:\Sample>java StaticBlockExample
Error: Main method not found in class StaticBlockExample, please define the main
method as: public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application

If you want to execute static block you need to have Main method and, static blocks of the class get executed before main method.

Example

 Live Demo

public class StaticBlockExample {
   static {
      System.out.println("This is static block");
   }
   public static void main(String args[]){
      System.out.println("This is main method");
   }
}

Output

This is static block
This is main method

Krishna Kasyap

Published on 03-Jul-2019 13:28:50

• Related Questions & Answers
• Non static blocks in Java.
• Demonstrate static variables, methods and blocks in Java
• Static blocks in Java with example
• When can we use Synchronized blocks in Java?
• When are static objects destroyed in C++?
• What are unreachable blocks in java?
• Where are static variables stored in C/C++?
• When are static C++ class members initialized?
• What are unreachable catch blocks in Java?
• Are values returned by static method are static in java?
• When to use static methods in Java?
• What are try, catch, finally blocks in Java?
• Functions that are executed before and after main() in C
• What are Orphan Blocks?
• Where and how to use static variable in swift?