java regular expression digits, letters, uppercase, lowercase

Question

I need a regular expression in Java with the following requirements:

• can only contain letters and digits
• must at least contain one digit
• must contain at least one upperCase letter AND one lowerCase letter

I have tried several expressions that don't work - this is the best so far:

(?=.*\\d)(?=.*[a-z])(?=.*[A-Z]).*

Answer 1

Anchor your regex, and don't use . which allows anything:

^(?=.*\\d)(?=.*[a-z])(?=.*[A-Z])[a-zA-Z0-9]*$

^$ matches beginning and end of string, [a-zA-Z0-9]* makes sure the characters are only those in the character class.