Integer.parseint异常

Question

The question was : Write a program that processes an input.txt file that contains data regarding ticket type followed by mileage covered and reports how many frequent-flier miles the person earns.

• 1 frequent flyer mile is earned for each mile traveled in coach.
• 2 frequent flyer miles are earned for each mile traveled in first class.
• 0 frequent flyer miles are earned on a discounted flight.

For example, given the data in input.txt below, your method must return 15600 (2*5000 + 1500 + 100 + 2*2000).

Input.txt:

firstclass 5000 coach 1500 coach
100 firstclass 2000 discount 300

My code gives me a problem with the parseint method. Any help would be appreciated :)

//InInteger class
import java.lang.NumberFormatException;
public class IsInteger {

public static  boolean IsaInteger (String s)throws  NumberFormatException 
{
    try
    {
        Integer.parseInt(s);//converts the string into an integer
        return true;
    }
    catch (NumberFormatException e)
    {
        return false;
    }
}

}

//main class

import java.io.*;
import java.util.StringTokenizer;


public class LA5ex2 {

public static void main(String[] args) throws FileNotFoundException {


BufferedReader input= new BufferedReader (new InputStreamReader (new FileInputStream("C:/Users/user/workspace/LA5ex2/input.txt")));
    String str;
    int TotalMiles=0;
    try {
        int mileage,lines=0;
         String check,copy=null;
         String word=null;
         boolean isString=false;

        while ((str = input.readLine()) != null)
        {
            lines++;
            StringTokenizer token = new StringTokenizer(str);
            while (token.hasMoreTokens()) 
            {
                if ((lines>1) && (isString))
                {
                    //do nothing
                }
                else    
                {word= token.nextToken();
                copy=word;}
              if (token.hasMoreTokens())
                  mileage= Integer.parseInt(token.nextToken());
              else
              {
                  if (!(IsInteger.IsaInteger(word)))
                  {
                      copy=word;
                      isString=true;
                  }

                  break;
              }
            if (copy.equals("firstclass"))
                TotalMiles+= (2*mileage);
            else if (copy.equals("coach"))
                TotalMiles+= (1*mileage);
            else if (copy.equals("discount"))
            TotalMiles+= (0*mileage);
            }
        }


System.out.println("Frequent-flier miles the person earns: "+ TotalMiles);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

}

Answer 1

This is the stacktrace that I get when running your code:

Exception in thread "main" java.lang.NumberFormatException: For input string: "firstclass"
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:481)
    at java.lang.Integer.parseInt(Integer.java:514)
    at LA5ex2.main(LA5ex2.java:30)

I assume this is the error that you mention in your comment. However, the NumberFormatException does not occur in your IsaInteger() method in the IsInteger class (where you try-catch it by returning true or false ), but in the LA5ex2 class (where you also try-catch it, but if it crashes, only the stacktrace gets printed). The exception occurs when Integer.parseInt() tries to parse the string firstclass as an integer, which of course fails:

if(token.hasMoreTokens()) mileage = Integer.parseInt(token.nextToken());

---

I rewrote your code in LA5ex2.java with two ArrayList s (to keep track of the various flier classes and the various mileages) using your IsaInteger method: import java.io.*; import java.util.ArrayList; import java.util.StringTokenizer;

public class LA5ex2 {

    public static void main(String[] args) throws FileNotFoundException {

        BufferedReader input = new BufferedReader(new InputStreamReader(new FileInputStream("input.txt")));
        String str = null;
        String token = null;
        int totalMiles = 0;
        int lines = 0;
        ArrayList<String> flierClasses = new ArrayList<String>();
        ArrayList<Integer> mileages = new ArrayList<Integer>();

        try {
            while((str = input.readLine()) != null) {
                lines++; // Why are we counting the lines, anyway?
                StringTokenizer tokenizer = new StringTokenizer(str);
                while(tokenizer.hasMoreTokens()) {
                    token = tokenizer.nextToken();

                    if(!(IsInteger.IsaInteger(token))) {
                        flierClasses.add(token); // if it's not an int, we assume it's a flier class
                    } else {
                        mileages.add(Integer.parseInt(token)); // if it's an int, it's a mileage
                    }
                }
            }
        } catch(NumberFormatException ex) {
            // TODO Auto-generated catch block
            ex.printStackTrace();
        } catch(IOException ex) {
            // TODO Auto-generated catch block
            ex.printStackTrace();
        }

        // Add everything up
        for(int i = 0; i < flierClasses.size(); i++) {
            totalMiles += calculateFlierMiles(flierClasses.get(i), mileages.get(i));
        }

        System.out.println("Frequent-flier miles the person earns: " + totalMiles);
    }

    private static int calculateFlierMiles(final String flierClass, final int mileage) {
        if(flierClass.equals("firstclass")) return(2 * mileage);
        else if(flierClass.equals("coach")) return(1 * mileage);
        else if(flierClass.equals("discount")) return(0 * mileage);
        return 0;
    }
}

This code gives me the desired output: Frequent-flier miles the person earns: 15600

Answer 2

I'm assuming the problem is in IsaInteger (which should be stylized as isAnInteger ). In that case, add a line that prints out the value of s before the try/catch and tell me what you get.

Also, why are you using tokens when you could use a BufferedReader and its nextLine() method?