Applying NumberValidator to a TextField will allow a number to be validated as a number and stored as a String. However, NumberValidator is not able to take a String and display it as a number. I think this should be a bidirectional process. An example of where this would be useful is the following:
I'd like to store a number as a String so I don't lose any prepending 0's (which RDBMSs love to throw out) when persisting the data. However, I do want to ensure that only a number is valid input.