Input mismatch when reading double from file

Question

I have to write a program that will read the names and balances from text file "balances.txt" and organize into a report that will then sum up the balances into a total. This is what the file contains:

JAKIE JOHNSON,2051.59 SAMUEL PAUL SMITH,10842.23 ELISE ELLISON,720.54

I had originally written the code which gave me exactly what I wanted, but was told not use loops, arrays, or parseDouble. I've now tried the following, but I keep getting an error every time I used nextDouble. The code:

import java.io.File; import java.text.NumberFormat; import java.text.DecimalFormat; import java.io.FileInputStream ; import java.io.FileNotFoundException ; import java.io.IOException ; import java.util.Scanner ; public class BankFile { public static void main(String[] args) throws IOException { Scanner fileIn = null; try { String filename = "balances.txt" ; File newFile = new File(filename); Scanner in = new Scanner(newFile); in.useDelimiter(","); String name = in.next(); System.out.println(name); // trying to see if first name will display double money = in.nextDouble(); System.out.println(money); // trying to see if first double will display } catch (FileNotFoundException e) { System.out.println("File not found."); System.exit(0); } } }

This is the output and exception stacktrace:

JAKIE JOHNSON Exception in thread "main" java.util.InputMismatchException at java.util.Scanner.throwFor(Scanner.java:864) at java.util.Scanner.next(Scanner.java:1485) at java.util.Scanner.nextDouble(Scanner.java:2413) at Lab2.main(BankFile.java:52) `

Do next, next, then nextDouble to advance the Scanner and receive the correct input. — Andrew Li
– Andrew Li, Commented Oct 12, 2016 at 1:55
we need to see the code that don't work, not the code that does work — Scary Wombat
– Scary Wombat, Commented Oct 12, 2016 at 1:57
sorry, I had forgotten to add the code I was struggling with — Derek
– Derek, Commented Oct 12, 2016 at 2:06
@Derek useDelimiter will return a new Scanner Object to use — Scary Wombat
– Scary Wombat, Commented Oct 12, 2016 at 2:20

Community · Accepted Answer · 2020-06-20 09:12:55Z

If you take a look at the Javadoc:

useDelimiter

public Scanner useDelimiter(String pattern)

Sets this scanner's delimiting pattern to a pattern constructed from the specified String.

Now if you take a look at how you do yours:

in.useDelimiter(",");

This will use commas as the delimiter, now let's take a look at your text file:

JAKIE JOHNSON,2051.59 SAMUEL PAUL SMITH,10842.23 ELISE ELLISON,720.54

At first it may seem that commas are fine, but since you've set the delimiter, this is what happens:

First you call in.next() which returns:

JAKIE JOHNSON,2051.59 ^^^^^^^^^^^^^

That's fine, but when you then call in.nextDouble(), the below happens:

JAKIE JOHNSON,2051.59 ^^^^^^^ SAMUEL PAUL SMITH,10842.23 ^^^^^^^^^^^^^^^^^

As you can see, the next line is also selected along with the double, which isn't a valid double. This causes Java to report an InputMismatchException, as the expected input isn't what you get - a string. To combat this, use a regular expression to also delimit newlines:

in.useDelimiter(",|\n");

This will match new-lines and commas, so it will delimit correctly. The pipe (|) means that it will delimit either. This will correctly output:

JAKIE JOHNSON 2051.59

The useDelimiter method returns a Scanner object, Doesn't this need to be used?

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