What are static blocks in Java?

When the static keyword is attached to a block of code, the block is called a static block.

Syntax

class Main{
   static {
        System.out.println("Hello World");
    }
}

Execution of static blocks

• Static blocks in Java are executed automatically when the class is loaded in memory.
• Static blocks are executed before the main() method.
• Static blocks are executed only once as the class file is loaded to memory.
• A class can have any number of static initialization blocks.
• The execution of multiple static blocks will be in the same sequence as written in the program. For example, the static blocks are executed from top to bottom.
• It’s possible to have only static blocks without a main() method up to Java version 1.5.
• Static blocks cannot access instance (non-static) variables and methods.

Advantages of static blocks

1. The logic to be executed during the class loading before executing the main() method can be in a static block.
2. Static blocks are mainly used to initialize the static variables.

Explanation

• Lines 3–5: We define a static block that prints Static Block 1.
• Lines 7–9: We define a static block that prints Static Block 2.
• Lines 11–13: We define the main method that prints hello world.

When the code is run, first the code in the static block is run then the main method is executed.