thread “main” java.lang.NumberFormatException: null

Question

I\'m a beginner to Java programming and I encounter the following exception:

Exception in thread \"main\" java.lang.NumberFormatException: null
            at ja         


        

Answer 1

This exception occurs if you try to convert a string to a number, where the string does not actually contain a number.

Example:

Integer.valueOf("10").intValue(); works, but Integer.valueOf("abcd").intValue() throws out the NumberFormatException.

Check your input file and make sure you're actually having a number there.

Line by Line debugger would be very useful here. Also use the good old System.out.println to see the value in id.