Java Blocks

Hey, welcome to the tutorial Blocks. Have you noticed that we have used “}” and “{“ braces very often in writing code?

Now, everything within { and } is collectively called a block.

Eg:

public class Blocks
{ // 1 begins
	public static void main(String[] args)
	{// 2begins
		
		{ //3 begins
			System.out.println("This is the 3rd block");
		} // 3 ends
		
		{ //4 begins
			System.out.println("This is the 4th block");
			
			{ // 5 begins
				System.out.println("This block 5 is inside the "
						+ "4th block");
			} //5 ends
			
		} //4 ends
	} //2 ends
} //1 ends

public class Blocks

{ // 1 begins

public static void main(String[] args)

{// 2begins

{ //3 begins

System.out.println("This is the 3rd block");

} // 3 ends

{ //4 begins

System.out.println("This is the 4th block");

{ // 5 begins

System.out.println("This block 5 is inside the "

+ "4th block");

} //5 ends

} //4 ends

} //2 ends

} //1 ends

This will be more clear to you with this picture:

So, if a block is started by {, then it definitely should end by writing }.

Try deleting one of } and see you will get an error.

Now can you see how these blocks are positioned relative to each other?

The 1^st block is the biggest guy and all the other blocks are started and ended inside it.

Have you noticed the gap between the ending } braces of 1^st block and 2^nd block?

They have a gap right? Similarly between 2 and 4 endings 4 and 5 endings, we can observe the same. This indentation helps us to understand the parent and child blocks.

This is not a rule. But a convention among programmers to keep things in an order.

3^rd block and 4^th block are independent of each other. Just like two children in a family. But the 5^th block is inside the 4^th block. So 5^th one is like a child of the 4^th block. It’s easy. Isn’t it?

OK. Now let me create a new variable inside the 3^rd block.

{ //3 begins
    int block3=234;
    System.out.println("This is the 3rd block");
    System.out.println(block3);
} // 3 ends

{ //3 begins

int block3=234;

System.out.println("This is the 3rd block");

System.out.println(block3);

} // 3 ends

The 2^nd println statement will print the value 234 in the console. But what happens if we try to write the same println statement in the 4^th block?? Let’s give a try…

{ //3 begins
	int block3=234;
	System.out.println("This is the 3rd block");
	System.out.println(block3);
} // 3 ends
		
{ //4 begins
	System.out.println(block3); // ERROR!!
	System.out.println("This is the 4th block");
			
        { // 5 begins
		System.out.println("This block 5 is inside the "
				+ "4th block");
	} //5 ends
			
} //4 ends

{ //3 begins

int block3=234;

System.out.println("This is the 3rd block");

System.out.println(block3);

} // 3 ends

{ //4 begins

System.out.println(block3); // ERROR!!

System.out.println("This is the 4th block");

{ // 5 begins

System.out.println("This block 5 is inside the "

+ "4th block");

} //5 ends

} //4 ends

An error occurs. Why?? I have told you that the blocks 3 and 4 are independent of each other. They don’t share a direct connection with each other.

So remember, any variable defined in 3^rd block is not visible to the 4^th. The integer variable block 3 is called a local variable.

But what happens if you make a new variable in 4^th block and print it in 5^th block??

{ //4 begins
			
	int block4=892;
	System.out.println("This is the 4th block");
			
	{ // 5 begins
		System.out.println("This block 5 is inside the "
				+ "4th block");
		System.out.println(block4); // works FINE :)
	} //5 ends
			
} //4 ends