Why am I getting InputMismatchException

Question

So far I have this   public double checkValueWithin int min  int max        double num      Scanner reader   new Scanner System in       num   reader nextDouble                                 while  num  lt  min    num  gt  max                             System out print  Invalid  Re-enter number               num   reader nextDouble                                       return num      and this   public void askForMarks         double marks     new double student       int index   0      Scanner reader   new Scanner System in       while  index  lt  student            System out print  Please enter a mark  0  30               marks index     double  checkValueWithin 0  30            index              When I test this  it can t take double number and I got this message   Exception in thread  main  java util InputMismatchException at java util Scanner throwFor Scanner java 909  at java util Scanner next Scanner java 1530  at java util Scanner nextDouble Scanner java 2456  at MarkingSystem checkValueWithin MarkingSystem java 25  at MarkingSystem askForMarks MarkingSystem java 44  at World main World java 6  Java Result  1   How do I fix this

User · Answer

Are you providing write input to the console ?

Scanner reader = new Scanner(System.in);
num = reader.nextDouble();

This is return double if you just enter number like 456. In case you enter a string or character instead,it will throw java.util.InputMismatchException when it tries to do num = reader.nextDouble() .

User · Answer

I encountered the same problem   Strange  but the reason was that the object Scanner interprets fractions depending on localization of system   If the current localization uses a comma to separate parts of the fractions  the fraction with the dot will turn into type String   Hence the error

User · Answer

Instead of using a dot  like  1 2  try to input like this  1 2

User · Answer

Here you can see the nature of Scanner      double nextDouble        Returns the next token as a double  If the next token is not a float or   is out of range  InputMismatchException is thrown    Try to catch the exception  try                catch  InputMismatchException e        System out print e getMessage       try to find out specific reason      UPDATE  CASE 1  I tried your code and there is nothing wrong with it  Your are getting that error because you must have entered String value  When I entered a numeric value  it runs without any errors  But once I entered String it throw the same Exception which you have mentioned in your question     CASE 2  You have entered something  which is out of range as I have mentioned above    I m really wondering what you could have tried to enter  In my system  it is running perfectly without changing a single line of code  Just copy as it is and try to compile and run it    import java util     public class Test       public static void main String    args            new Test   askForMarks 5              public void askForMarks int student            double marks     new double student           int index   0          Scanner reader   new Scanner System in           while  index  lt  student                System out print  Please enter a mark  0  30                   marks index     double  checkValueWithin 0  30                index                         public double checkValueWithin int min  int max            double num          Scanner reader   new Scanner System in           num   reader nextDouble                                     while  num  lt  min    num  gt  max                                 System out print  Invalid  Re-enter number                   num   reader nextDouble                                                 return num            As you said  you have tried to enter 1 0  2 8 and etc  Please try with this code   Note   Please enter number one by one  on separate lines  I mean  enter 2 7  press enter and then enter second number  e g  6 7

User · Answer

Since you have the manual user input loop  after the scanner has read your first input it will pass the carriage return into the next line which will also be read  of course  that is not what you wanted   You can try this  try                catch  InputMismatchException e        reader next         or alternatively  you can consume that carriage return before reading your next double input by calling      reader next

[java] Why am I getting InputMismatchException?

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