How to Fix the Input Mismatch Exception in Java?

p>The InputMismatchException is a runtime exception in Java that is thrown by a Scanner object to indicate that a retrieved token does not match the pattern for the expected type, or that the token is out of range for the expected type.

Since InputMismatchException is an unchecked exception, it does not need to be declared in the throws clause of a method or constructor.

What Causes InputMismatchException

The InputMismatchException generally occurs when working with Java programs that prompt users for input using the Scanner class. The exception can occur when the input is invalid for the expected type. The input either does not match the pattern for the expected type, or is out of range.

For example, if a program expects an Integer value for an input but the user enters a String value instead, an InputMismatchException is thrown.

InputMismatchException Example

Here is an example of an InputMismatchException thrown when a String is entered as input to a Scanner that expects an integer:

import java.util.Scanner;

public class InputMismatchExceptionExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter an integer: ");

        int integer = scanner.nextInt();
        scanner.close();

        System.out.println("You entered: " + integer);
    }
}

In the above code, the user is prompted for an integer as input. The Scanner.nextInt() method is used to retrieve the value, which expects an integer as input. If the user enters a String value instead of an integer, an InputMismatchException is thrown:

Enter an integer:
String
Exception in thread "main" java.util.InputMismatchException
    at java.base/java.util.Scanner.throwFor(Scanner.java:939)
    at java.base/java.util.Scanner.next(Scanner.java:1594)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
    at InputMismatchExceptionExample.main(InputMismatchExceptionExample.java:8)

How to Fix InputMismatchException

To avoid the InputMismatchException, it should be ensured that the input for a Scanner object is of the correct type and is valid for the expected type. If the exception is thrown, the format of the input data should be checked and fixed for the application to execute successfully.

In the above example, if an integer is entered as input to the Scanner object, the InputMismatchException does not occur and the program executes successfully:

Enter an integer:
5
You entered: 5

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