Password Generator, generate password of desired length
Note: The 65 comes from the CHARACTER_SET length, which I have found out before.


It's 65 at the moment. But what if you want to support more or less characters? A different character set? You'd have to change those hard-coded values every time.

CHARACTER_SET.charAt(random.nextInt(65)


Can be replaced by:

CHARACTER_SET.charAt(random.nextInt(CHARACTER_SET.length())


There is one more hard-coded value in your code.

System.out.println(generatePassword(20));


Extract the 20 to it's own variable. This allows you to extend your program to, for example, ask for user input and use that value instead. Perhaps the user prefers 16 or 28.