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);
        }
  }

}

Java Local Variables

Declaration

Declaration of local variables is similar to C/C++. A local variable can be declared anywhere in a method or block and can be initialized during declaration. It is not must to initialize a local variable during declaration but it must be initialized in the same block in which it is declared before the first use. More than one variables of the same type can be declared using single declaration statement by separating the variable names with comma.

Examples:

long x, y, z;
float d;
int a=0, b=10, c=5;

Example: The following program demonstrates the declaration and use of local variables.

Step 1: Open a new file named Local.java and type the following Java Program

class LocalVarDemo{
   
     public static void main(String args[]){
          int num1;
          int num2 = 10;
          int sum, product;
          float f1 = 3.5f; f2 = 6.9f, sumf;

          num1 = 15;
          sum = num1+num2;
          System.out.println("Sum of two integer values = " + sum);
         
          sumf = f1+f2;
          System.out.println("Sum of two floating point values = " + sumf);
     }
}

Step 2: Compile above Java program using command javac Local.java in the command window.

Step 3: Execute the program using command java LocalVarDemo in the command window.

The output of the program will be:

          Sum of two integer values = 25
          Sum of two floating point values = 10.4