How to Continue Past Inputmismatchexception in Java

The error code that reads exception in thread "main" java.util.inputmismatchexception happens when your Java application takes incorrect input from your users. It can be a tough one to deal with but don't fret, we'll teach you how to fix the error. Continue reading this guide and we'll demystify why this error occurs and provide other information that will help you understand the error.

Contents

• Why Do You Have the Inputmismatchexception Error?
• How To Fix the Inputmismatchexception Error
• Thematic Section About the Inputmismatchexception Error
  • – What Are Java Exceptions?
  • – Why Do We Need To Handle Exceptions?
  • – What Are the Different Exceptions in Java?
  • – How Is an Exception Handled in Java?
  • – How Do You Deal With Inputmismatchexception?
  • – Is Inputmismatch a Checked Exception?
• Conclusion

Why Do You Have the Inputmismatchexception Error?

You are getting the InputMismatchException because your user entered invalid data. For example, InputMismatchException will occur if your application receives a string instead of a number.

In the next Java code, we have a Scanner class that reads input from users. The Scanner class accepts String objects, InputStream, File, and Path. Behind the scenes, it uses regular expressions to read the data. Here, we used the Scanner class to request that the user enter a number.

import java.util.Scanner;
public class Main {
public static void main (String arg[]) {
int num;
// Setup a scanner to read the user input
Scanner in = new Scanner(System.in);
// Tell the user to enter an integer value
System.out.print("Enter an integer value: ");
// Get ready to read the integer
num = in.nextInt();
// Show the user what they've entered
System.out.println("You entered the number " + num);
}

So run the code and enter the number 50. the application will return the sentence that reads: You entered the number 50, which is what you'd expect. However, when you run the code again, enter a string like "Hello," you'll get the Stack Trace of the error below.

$ java Main.java
Enter an integer value: Hello
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 com.mycompany.company.Main.main(Main.java:17)

How To Fix the Inputmismatchexception Error

You can fix the InputMismatchException error by implementing error checking in your code. Meanwhile, the error checking should display a message instead of an InputMismatchException error, so instead of InputMismatchException error details, your users should see a custom message. An example of such a message is: Please enter an integer.

The next code block is the same as the previous one. However, we've modified the code. The modification will handle InputMismatchException errors when your user enters invalid data.

The following are the modifications to the code:

• We've initialized the num variable to zero.
• We've set up a guard variable that we'll use to track if the user has entered the right data.
• There is a while loop that will always run as long as the user enters an invalid input.
• We've set up a try and catch block.
• Within the try and catch block, we read the user input as a string. Afterward, we convert it to an integer.
• We switch the guard variable to TRUE once the user enters the correct data. This will break the loop.

After all this, every time there is an exception, we tell the user to enter an integer value. This prevents the user from seeing the InputMismatchException error.

The following code is the implementation of these steps:

import java.util.Scanner;
public class Main {
public static void main (String arg[]) {
int num = 0;
String strInput;
// A guard variable that'll keep track whether
// the user has entered a valid input
boolean isValid = false;
// Setup a new Scanner instance to take
// input from the user
Scanner userInput = new Scanner(System.in);
while(isValid == false) { // Invalid user input
System.out.print("Enter an integer value: ");
strInput = userInput.nextLine();
try{
num = Integer.parseInt(strInput);
// We have good data, so, break out of the loop.
isValid = true;
} catch(NumberFormatException e) {
System.out.println("Error – Please enter an integer value");
}
}
// Show the user what they've entered.
// The code will only execute to this point
// if everything is OK.
System.out.println("You entered the number " + num);
}
}

The following is a sample session where the user keeps entering an invalid value. Every time they do that, we tell them to enter the correct data. Because of this, the while loop continues until they enter the correct data.

$ java Main.java
Enter an integer value: uy
Error – enter an integer value
Enter an integer value: tr
Error – enter an integer value
Enter an integer value: 9.8
Error – enter an integer value
Enter an integer value: 54
You entered the number 54

Thematic Section About the Inputmismatchexception Error

In this section, we'll answer questions that you have about InputMismatchException. We understand that your questions need detailed answers, so don't worry as we'll explain everything in great detail.

– What Are Java Exceptions?

Java exceptions are events that result in the disruption of the flow of application execution. The exception can happen either at compile-time or run-time.

In this article, we have shown you that an invalid input causes an exception. The following are other situations that can cause an exception in your Java program:

• The program could not find a file that it needs.
• There was a drop in network connection during communication.
• These situations could arise as a result of a programming error or the application user.

– Why Do We Need To Handle Exceptions?

We need to handle exceptions to prevent the abnormal termination of a program, which is necessary to keep the program running despite an interruption in its normal flow. From a security consideration, your application can throw an exception during its execution. With this, a curious user can predict the code structure of the application due to the error messages.

For example, an error message that reads: "Please enter a valid input" is better than "Exception in thread "main" java.util.InputMismatchException at java.base/java.util.Scanner.throwFor(Scanner.java:939)".

– What Are the Different Exceptions in Java?

RuntimeException, NumberFormatException, and ArithmeticException are some examples of different exceptions in Java. The following are the different exceptions in Java in more detail:

• RuntimeException: This happens during runtime.
• NumberFormatException: The JVM will raise this exception when there is a problem during the conversion of string to a numeric format.
• ArithmeticException: This arises as a result of an arithmetic error — for example, a division of 10 by zero.
• ClassNotFoundException: Trying to access an undefined class will raise the ClassNotFoundException.
• IOException: An error in a input and output operation will raise the IOException.
• FileNotFoundException: This exception happens when you can not access a file.
• InterruptedException: This is raised when an interruption occurs during thread operations.
• NoSuchFieldException: A missing field or variable name in a class will raise the NoSuchFieldException.
• NoSuchMethodException: An attempt to access an undefined method will cause NoSuchMethodException.
• NullPointerException: A null object causes this exception.
• StringIndexOutOfBoundsExceptio: The String class will throw this exception when an error occurs.
• ArrayIndexOutOfBoundsException: Accessing an array with an invalid index causes this exception. This index can be negative or greater than the size of the array.

– How Is an Exception Handled in Java?

You can handle an exception using a try-catch block; all you have to do is make sure that you place any code that can raise an exception in the try block. Meanwhile, the code that will catch the exception should be in the catch block. With this, you are better prepared for any exception during your program execution.

– How Do You Deal With Inputmismatchexception?

You can deal with InputMismatchException by setting up an input validation routine. The validation routine should ensure that your user enters valid inputs. At the same time, when an exception occurs, the validation routine should handle it.

In this article, we've shown you how to handle exceptions in our examples. As a reminder, the following is the structure of how to handle InputMismatchException.

import java.util.Scanner;
public class Main {
public static void main (String arg[]) {
try {
// Place code that can raise an
// Exception here
}catch(NumberFormatException e) {
// Enter a generic message in place of
// Exception
}
}
}

– Is Inputmismatch a Checked Exception?

No, InputMismatchException is an unchecked exception. Unchecked exceptions are exceptions that are not checked at compile time. Other examples of unchecked exceptions are RuntimeException and ArithmeticException.

In this article, we've shown you how to deal with InputMismatchException. However, we'll reiterate why InputMismatchException is an unchecked exception. In the Java code below, we attempted to divide 10 by zero, so when you compile the code, you will not receive any error messages.

However, when you run the code, you'll get the following error message detailed below. This shows InputMismatchException is an unchecked exception just like ArithmeticException.

public class Main {
public static void main (String arg[]) {
int first_num = 0;
int second_num = 10;
int result = second_num / first_num;
}
}

The Stack Trace of the error:

$ java Main.java
Exception in thread "main" java.lang.ArithmeticException: / by zero
at com.mycompany.company.Main.main(Main.java:50)

Conclusion

This article explained how to fix the InputMismatchException error in your Java programs, and you also learned more information about InputMismatchException in the thematic section. The following is a summary of everything we've discussed:

• InputMismatchException happens when your Java application users supply the wrong input.
• You can deal with InputMismatchException using try and catch block.
• InputMisMatchException is part of Java Exceptions. Others include the likes of ArithmeticException and NumberFormatException.
• Handling exceptions in your program prevents abnormal termination during execution.
• InputMismatchException is an unchecked exception.

At this stage, you can now handle InputMismatchException in your Java applications with ease! Be sure to refer to our guide to keep yourself up to date.

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