Exceptions

If the input characters can be converted into a double, then that is done, even if the input characters lack a decimal point.

If the input starts with characters that can NOT be converted into a double, then Java throws and exception and this program halts. (A later chapter will discuss how to deal with exceptions.) For example:

C:\temp>java DoubleDouble
Enter a double: rats
Exception in thread "main" java.util.InputMismatchException
        at java.util.Scanner.throwFor(Unknown Source)
        at java.util.Scanner.next(Unknown Source)
        at java.util.Scanner.nextDouble(Unknown Source)
        at DoubleDouble.main(DoubleDouble.java:14)

If the input starts with characters that can be converted into a double, and is followed by one or more spaces, then those characters are converted regardless of what follows. For example:

C:\temp>java DoubleDouble
Enter a double: 3.14 and more characters
value: 3.14 twice value: 6.28

A subsequent call to a method that expects digits (such as nextDouble()) will try to convert the "and" and will throw an exception.

C:\temp>java DoubleDouble
Enter a double: -97.65

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