mortgage calculator (java.util.InputMismatchException)

hello i have a problem when following a tutorial in youtube (the code is in java, i am using intelliji idea)

import java.text.NumberFormat;
import java.util.Locale;
import java.util.Scanner;

public class Main {
    public static void main(String[] arg) {
        final byte MONTHS_IN_YEAR = 12;
        final byte PERCENT = 100;
        Scanner scanner = new Scanner(System.in);

        System.out.print("Principal: ");
        int principal = scanner.nextInt();

        System.out.print("Annual Interest Rate: ");
        float annualInterest = scanner.nextFloat();
        float monthlyInterest = annualInterest / PERCENT / MONTHS_IN_YEAR;

        System.out.print("Period (Years): ");
        byte years = scanner.nextByte();
        int numberOfPayments = years * MONTHS_IN_YEAR;

        double mortgage = principal
                * (monthlyInterest * Math.pow(1 + monthlyInterest, numberOfPayments))
                / (Math.pow(1 + monthlyInterest, numberOfPayments) - 1);
        String mortgageFormatted = NumberFormat.getCurrencyInstance(Locale.US).format(mortgage);
        System.out.println("Mortgage: " + mortgageFormatted);
    }
}

The problem is when i input the Annual Interest Rate (like 3.92) it give me the following error:

Exception in thread "main" java.util.InputMismatchException
	at java.base/java.util.Scanner.throwFor(Scanner.java:947)
	at java.base/java.util.Scanner.next(Scanner.java:1602)
	at java.base/java.util.Scanner.nextFloat(Scanner.java:2505)
	at com.codewithtamer.Main.main(Main.java:17)

And thank you for helping a beginner like me :), + i think i somehow messed up the format of this post sorry

If you want to use a Locale with your Scanner which is different to your default locale (the one Java gets from the operating system) you can do this:

class App {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println(s.locale());
        s.useLocale(Locale.US);
        System.out.println(s.nextFloat());
    }
}

That will show your current locale (for me it prints en_AU) and then sets the scanner to use a different locale.

Locale.US with require . as a decimal separator, Locale.FRANCE requires , and so on.

Unfortunately in some versions of some IDEs the java.util.Scanner reads decimals in European mode (i.e. with a decimal comma). This has been observed in Eclipse and Netbeans as suggested by this StackOverflow Q&A (https://stackoverflow.com/questions/28997094/scanner-next-throws-java-util-inputmismatchexception-for-float-but-not-for-in). You could look into changing the version of your IDE, or you could write the percent with a comma (not ideal), or you can instead rely on Float.parseFloat() such as in the following:

System.out.print("Annual Interest Rate: ");
float annualInterest = Float.parseFloat(scanner.next());
float monthlyInterest = annualInterest / PERCENT / MONTHS_IN_YEAR;

This should work with a decimal point as Float.parseFloat() is not location-dependent and always expects a decimal point.

As per the JavaDoc for Scanner#nextFloat,

> "... Throws [an] InputMismatchException if the next token does not match the Float regular expression, or is out of range ...".

And, the same goes for the nextInt method—the exception is thrown if the value is not an integer value.

Although, as a note, you can use the nextFloat to capture integer values.

For example,

Principal: 1
Annual Interest Rate: 2
Period (Years): 3
Mortgage: $0.03

And,

Principal: 1.23
Exception in thread "main" java.util.InputMismatchException
	at java.base/java.util.Scanner.throwFor(Scanner.java:947)
	at java.base/java.util.Scanner.next(Scanner.java:1602)
	at java.base/java.util.Scanner.nextInt(Scanner.java:2267)
	at java.base/java.util.Scanner.nextInt(Scanner.java:2221)
	at Example.main(Example.java:14)