Blocks in Java

What are Blocks in Java?

• Blocks are the special type of containers in java language.
• It acts as a container for executable java statements.
• Blocks mainly perform special type of operations. e.g. Database connectivity, Server Configuration etc.
• Blocks are mainly classified into two types:
  • Static Block
  • Non static Block

Static Blocks

• We have to declare static blocks by using static keywords.
• We use static block mainly to develop business logic where outcome of the logic is same for all the users and it executes only once in a application lifecycle.
• If java class contains static block and main method then static block executes before the main method at the time of class loading.
• It is possible to create multiple static blocks inside the single java class.
• We can initialize static variables inside the static block.

Non static Blocks

• We declare non static blocks without using the static keyword.
• We use non static blocks to develop business logic which is common for all objects also, which executes multiple times in an application lifecycle.
• Non static blocks execute at the time of object creation.
• It is possible to declare multiple non static blocks inside the single java class.
• We can initialize non static as well as static members inside the non static block.

Example:

public class Demo {
    //Syntax for static block
    static{
        //Executes at the time of class loading
        System.out.println("STATIC BLOCK");
    }

    public static void main(String[] args) {
        System.out.println("MAIN METHOD");
        Demo d1=new Demo();
    }
    //Syntax for non static block
    {
        //Executes at the time of object creation
        System.out.println("NON STATIC BLOCK");
    }
}

Output:

STATIC BLOCK
MAIN METHOD
NON STATIC BLOCK

Difference between Methods and Blocks in Java

• Methods in Java are responsible to perform normal business logic operation whereas, blocks perform special operations.
• Developer is responsible to call the method explicitly for execution while blocks will be automatically executed by JVM.
• Every method is having an identity but blocks do not have any identity.
• We can pass parameters by using methods but it is not possible to pass input parameters for blocks.
• It is possible to return value from method whereas you cannot return a value from block.