This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
In a login screen, when a user submits a blank page without entering a username and password, it should show an error message. What methods should I use to check that the fields are blank when submitted?
What sort of object are you using for your input? A JTextField? If you are checking the input with the getText() methods, you get a String. There are methods for checking the length of Strings, so you can send out an error message if the length comes to zero.