Q:

Having an issue with a variable in java

Having an issue compiling. The compiler is saying a variable is not used even though I use it on line 25.

Error:
  [line: 21]
  Warning: The value of the local variable pay is not used

// CreatePayroll.java takes wages and hours from file and creates pay file.
import java.util.*;
import java.io.*;
public class CreatePayroll {
  public static void main(String[] args) {
    try{
//Scanner for input file
      File inputFile = new File("employees.txt");
      Scanner fin = new Scanner(inputFile);
//Printwriter for output file
      File outputFile= new File("payroll.txt");
      PrintWriter fout = new PrintWriter(outputFile);
//read input file creates new file
      while ( fin.hasNextLine() ) {
        String firstName = fin.next();
        String lastName = fin.next();
        double wage = fin.nextDouble();
        double hours = fin.nextDouble();
        //Calculates pay
        if (hours > 40) {
          double pay = (wage*40)+((hours-40)*(wage*1.5));
        } else {
          double pay = wage*hours;
//last line to print to out file
          fout.println(firstName + " " + lastName + " $" + pay);
        }
      }
//cleanup
      fin.close();
      fout.close();
      System.out.print("DONE! See 'payroll.txt'.");
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

A:

You have a severe scope problem: you're declaring the pay variable twice inside your both the if and else statements, meaning that these very local variables are only visible within these blocks. Don't do that. Declare pay above the if/else block so it can be used throughout the method.
so change:
if (hours > 40) {
    double pay = (wage*40)+((hours-40)*(wage*1.5));
} else {
    double pay = wage*hours;
    //last line to print to out file
    fout.println(firstName + " " + lastName + " $" + pay);
}

to:
// declare pay prior to the if/else blocks
double pay = 0.0;
if (hours > 40) {
     pay = (wage*40)+((hours-40)*(wage*1.5));
} else {
     pay = wage*hours;
}

// get the line below **out** of the else block
fout.println(firstName + " " + lastName + " $" + pay);

