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Control Statements > Blocks of code >
Siva Nookala - 12 Apr 2016
Scope Of Variables - in Nested/Multiple Blocks in Java States that variables declared in outer blocks will be accessible in inner blocks, where as variables declared in inner blocks can not be used outside of the block.

Nestedmultiple blocks
class NestedMultipleBlocks
{
    public static void main(String arg[])
    {
        int x = 10;    // LINE A
        int a = 20;    // LINE B
        
        System.out.println("x = " + x);
        
        {
            // INNER BLOCK 1
            int y = x * 2;
            System.out.println("y in inner block 1 = " + y );
            x = 50;
            System.out.println("x in inner block 1 = " + x );
        }
        // LINE C
        
        // System.out.println("y = " + y); // Won't work
        int z = 20;
        System.out.println("z = " + z);
        
        {
            // INNER BLOCK 2
            int y = x * 3;
            System.out.println("y in inner block 2 = " + y );
            z = y;
            System.out.println("z in inner block 2 = " + z );
        }
        
        // int a = 70;     // Won't work   // LINE D
        
        System.out.println("x after the blocks = " + x);
        
        // System.out.println("y = " + y); // Won't work // LINE E
        
        System.out.println("z after the blocks = " + z); // LINE F
    
    }
}
OUTPUT

x = 10
y in inner block 1 = 20
x in inner block 1 = 50
z = 20
y in inner block 2 = 150
z in inner block 2 = 150
x after the blocks = 50
z after the blocks = 150

DESCRIPTION

Here x is valid in all lines below LINE A, a is valid in all lines below LINE B.
y declared in INNER BLOCK 1 is valid only inside that block and is not valid after LINE C.
y can be declared again in INNER BLOCK 2 and will be valid only in that block.
z declared above INNER BLOCK 2 is valid inside INNER BLOCK 2 as well as after the block i.e. in LINE F.
Redeclaring a again in LINE D will not work since there is already a variable with the same name in the scope.
Trying to print y after INNER BLOCK 1 or INNER BLOCK 2 will not work since the scope is restricted only to inside the blocks.

THINGS TO TRY
  • Uncomment - the statement int a = 70; at LINE D to see the error - "a is already defined in main"
  • Uncomment - the statement System.out.println("y = " + y); at LINE E to see the error - "cannot find symbol"
  • Change int y = x * 3; to y = x * 3; in LINE C1 to see the error - "cannot find symbol"

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