Java Local variable Scope and Life Time

A local variable's scope is restricted to the block or method in which it is declared. It can be accessed only in the block/method in which it is declared, from the point of declaration till the end of the block/method.

A local variable comes into existence when the code of the block/method containing the declaration is executed and the declaration is encountered during execution. The variable exists only till the flow of control reaches to the end of the block/method containing it.

One important scope rule in Java that a local variable in some inner block can not hide the variable of the same name in the outer block. This is allowed in C++ and the reference to outer block variables is resolved using scope resolution operator but it is not allowed in Java.

Example: The following program will not compile.

class ScopeDemo{
   
    public static void main(String args[]){

        int i=5;
        {
            int i=10;
            System.out.println(i);
        }
    }
}

On compiling this program you will see following error messages:

i is already defined in main(java.lang.String[])

The reason is that i in the inner block hides i of the outer block which is not allowed in Java.

The following program will compile successfully though local variable  i has multiple declarations. The reason is that both the blocks in which i is declared are at the same level.

class ScopeDemo1{
   
    public static void main(String args[]){

        for(int i=0;i<5;i++){
            System.out.println(i);
        }

        for(int i=0;i<7;i++){
            System.out.println(i);
        }
  }

}