How to get Scanner to read next line of numbers?

Question

I am new to java and programming. I have sort of a grasp on the concept but not entirely sure. This problem uses a scanner to read from another file to get information on amount of energy produced.

import java.util.Scanner;
import java.io.File;

public class HJUnit3
{
 public static void main(String[] args) throws Exception
 {
//   Scanner stdIn = new Scanner(System.in);
   Scanner stdIn = new Scanner(new File("energyProduced.txt"));
        stdIn.nextLine();
  double energy;
  energy = stdIn.nextLine();
   int systemsCost;  //Total Systems Cost
   double ttlEnergy;  //Total energy produced in a week
   double savingsWeek;  //Total savings for one week
   double savingsDay;  //Total savings for one day
   double recoupDay;  //Days to recoup
   double recoupYear; //Years to recoup
   final double electricCost = 0.085;
   
   systemsCost = (savingsWeek * energy);
   System.out.println("Total System Cost = $" + systemsCost );
   System.out.println("Total Energy Produced in one week" + (energy * 7) + "Kwh");
   savingsWeek = (ttlEnergy * electricCost);
   System.out.println("Total Savings for one week =" + savingsWeek);
   savingsDay = (savingsWeek / 7);
   System.out.println("Total Savings for one day =" + savingsDay);
   recoupDay = (systemsCost / savingsDay);
   System.out.println("Days to recoup cost(truncated)" + recoupDay);
   recoupYear = (recoupDay / 365);
   System.out.println("Years to recoup cost(truncated)");
 } // end main
} // end HJUnit3 class

It gives me this error "error: incompatible types: String cannot be converted to double energy = stdIn.next();"

and this "error: incompatible types: possible lossy conversion from double to int systemsCost = (savingsWeek * energy);"

What did I do wrong, not really sure.

EDIT So I got the program to work but in the program produces only one set of answers from the .txt file but the file has more numbers and I'm not sure what to add to make it read the next line.

import java.util.Scanner;
import java.io.File;

public class HJUnit3
{
 public static void main(String[] args) throws Exception
 {
//   Scanner stdIn = new Scanner(System.in);
   Scanner stdIn = new Scanner(new File("energyProduced.txt"));
        stdIn.nextDouble();
  double energy;
  energy = stdIn.nextDouble();
   int systemsCost;  //Total Systems Cost
   double ttlEnergy; //Total energy produced in a week
   double savingsWeek; //Total savings for one week
   double savingsDay;  //Total savings for one day
   double recoupDay;  //Days to recoup
   double recoupYear; //Years to recoup
   final double electricCost = 0.085;
//
   
   ttlEnergy = (energy * 7);
   savingsWeek = (ttlEnergy * electricCost);
   savingsDay = (savingsWeek / 7);
   systemsCost = (int) (savingsWeek * energy);
   recoupDay = (systemsCost / savingsDay);
   recoupYear = (recoupDay / 365);
 
 System.out.println("Total System Cost = $" + systemsCost );
 System.out.println("Total Energy Produced in one week" + (ttlEnergy) + "Kwh");   
    System.out.println("Total Savings for one week =" + savingsWeek);
    System.out.println("Total Savings for one day =" + savingsDay);
    System.out.println("Days to recoup cost(truncated)" + recoupDay);
    System.out.println("Years to recoup cost(truncated)" + recoupYear);
 } // end main
} // end HJUnit3 class

The .txt file is like a bunch of numbers going down a column

Answer 1

The compiler says that a String cannot be converted into a Double. That's the problem. You're saying double energy = stdIn.nextLine(), but Scanner#nextLine() returns a String. Instead, you either want to convert it to a Double (Double.parseDouble(String)), or you could call stdIn.nextDouble(). http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html

Answer 2

You may need to brush up on your "datatypes" skills, because Java is a strongly typed language :-).

The error

error: incompatible types: String cannot be converted to double energy = stdIn.next();

means that the value returned by stdIn.next() has a datatype of "string", which does not match the datatype of the variable "energy", because "energy" is not a string. It is a "double".

You convert the value returned by stdIn.next() to a double by using

energy = Double.parseDouble(stdIn.next());

Beware that this will throw an exception when the string returned by stdIn.next() characters such as alphabets.

For your second error, why do you want systemsCost variable to be an integer? Do you want it to always be a rounded number? If so, then you need to round the result of the expression "savingsWeek * energy" to the nearest whole number, and then convert it into an integer. On the other hand, if you don't necessarily want systemsCost to be an integer, just declare it as a double.