Imagine you are developing a software package for Amazon.com that requires users to enter their own passwords. Your software requires that users’ passwords meet the following criteria: 

• 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 one 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.