Your task is to read a file containing arithmetic instructions such as Each inst

Question

Your task is to read a file containing arithmetic instructions such as

Each instruction contains an integer, an operator (+, -, or *), and another integer.

Return an array list of the results. If there is any error, throw an IOException.

Complete the following file:

Arithmetic.java

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

public class Arithmetic
{
/**
This class reads a file containing arithmetic expressions and returns an
array list of the results.
@param filename the file name
@return a list of results
*/
public static ArrayList<Integer> read(String filename) throws IOException
{
. . .
}

// This method checks your work. Do not touch it.

public static String check(String filename)
{
try
{
return read(filename).toString();
}
catch (IOException ex)
{
return "I/O exception thrown";
}
catch (Exception ex)
{
return ex.getClass().getName();
}
}
}   

(P.S. where the "..." is where I have to add new code can't change anything else"

Explanation / Answer

Hi ,

Kindly find below program as well text file.

arithmetic_instructions.txt

=================

3 + 4
4 - 10
7 * 11
55 - 10

=====================

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;

public class Arithmetic {
   /**
   * This class reads a file containing arithmetic expressions and returns an
   * array list of the results.
   *
   * @param filename
   * the file name
   * @return a list of results
   */
   public static ArrayList<Double> read(String filename) throws IOException {
       ArrayList<Double> result = new ArrayList<Double>();

       BufferedReader br = null;

       try {

           String sCurrentLine;

           br = new BufferedReader(new FileReader(filename));
           while ((sCurrentLine = br.readLine()) != null) {
                   System.out.println(sCurrentLine);
                   result.add((Double) evaluate(sCurrentLine));              
           }

       } catch (IOException e) {
           e.printStackTrace();
       } finally {
           try {
               if (br != null)
                   br.close();
           } catch (IOException ex) {
               ex.printStackTrace();
           }
       }

       return result;
   }

   public static Double evaluate(String expression){
       String[] parts =expression.split("(?=[\*|\+|-])|(?<=[\*|\+|-])"); //Regex to find operator
       Double result = Double.parseDouble(parts[0]);

       for (int i = 1; i < parts.length; i += 2) {
       String op = parts[i];
       double val = Double.parseDouble(parts[i+1]);
       switch (op) {
       case "+" :
       result += val;
       break;
       case "-" :
       result -= val;
       break;
       case "*" :
       result *= val;
       break;
       }
       }
       return result;
   }
   // This method checks your work. Do not touch it.

   public static String check(String filename) {
       try {
           return read(filename).toString();
       } catch (IOException ex) {
           return "I/O exception thrown";
       } catch (Exception ex) {
           return ex.getClass().getName();
       }
   }

   public static void main(String args[]) {
       System.out.println(check("arithmetic_instructions.txt"));
   }
}

Let me know if you still have any questions.

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