Authenticating A Password With Criteria

I have a question but dont know how I could verify the criterias..

The password should be at least six characters long
The password should contain at least one uppercase and at least one lowercase letter
The password should have at least on digit

Write a class that verifies that a password meets the stated criteria. Demonstrate the class in a program that allows the user to enter a password and then displays a message indicating whether it is valid or not.

I have not created a class because I really have no clue what to write in this case. My main method is:

import java.util.Scanner; // Needed for the Scanner class
 public class Password {
public static void main(String[] args) {
// Create a Scanner object to read input.
Scanner keyboard = new Scanner(System.in);
String input;// To hold the input

[Code] .....