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InputMismatchException in Java

beginner· Exceptions · Error Handling

Problem

An InputMismatchException is thrown when a Scanner method like nextInt() is called but the next token in its input isn't actually formatted as that type.

Use Scanner.nextInt() to read a token that isn't a valid integer, and handle the resulting exception.

Input

new Scanner("abc").nextInt()

Output

Error: Expected an integer but the input wasn't one

Java Program

Java

import java.util.InputMismatchException;
import java.util.Scanner;

public class InputMismatchExceptionDemo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner("abc");
        try {
            int number = scanner.nextInt(); // "abc" isn't formatted as an integer
            System.out.println("Number: " + number);
        } catch (InputMismatchException e) {
            System.out.println("Error: Expected an integer but the input wasn't one");
        }
    }
}

▶ Run Code

Output

Error: Expected an integer but the input wasn't one

Core Logic

Wrapping the risky nextInt() call in try-catch lets a badly-formatted token be caught and reported instead of crashing the program.

How It Works

1new Scanner("abc") builds a Scanner reading from the fixed string "abc" instead of real console input, keeping the example self-contained and repeatable.
2scanner.nextInt() tries to read the next token and interpret it as an int.
3Since "abc" isn't formatted as an integer, this throws an InputMismatchException rather than returning a value.
4The catch (InputMismatchException e) block catches it and prints a message instead of letting the program crash.

Calling nextInt() on a scanner reading "abc" throws immediately, caught and printed as "Error: Expected an integer but the input wasn't one".

💡

Key Point: Scanner can read from any source of text, not just the console — building one directly from a String, like here, is a common way to test input-parsing logic without needing real keyboard input.

Key Concepts

try / catchScannerInputMismatchException

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