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 < min || num > 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 < 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?
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 < 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 < min || num > 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
).
Instead of using a dot, like: 1.2, try to input like this: 1,2.
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 ...
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()
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() .
来源:https://stackoverflow.com/questions/14027537/why-am-i-getting-inputmismatchexception