validating a string for numbers and letters?

[lockmac]

Hi. I need to validate a string. My string is 7 characters long (which i have made validation for) but i need my string to validate so that the first 3 characters are letters and the next 4 characters are numbers..

any ideas how to do this? ive been told to use substring but i dont know how to use this to check if they are numbers or whether they are letters.

many thanks

[vata2999]

I think you need Regular Expression but i don't know how use regular Expression in java See below link
[link]
Regular Expressions and the Java Programming Language
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