Preparing to develop J2EE web application

J2EE Multi-tiered Applications are distributed over three locations:

client machines:Client Tier Thin Clients

without locally stored application software, providing presentation but no data processing(which occurs on the server), do not query databases or execute business logic, all those functions are encapsulated in beans executing in the J2EE server.

THin  clients examples: Web browsers and mobile phone displays.

Thick Clientsperform complex functions usually has a GUI(Graphical User Interface), keep functionality on the client machine rather than the server.J2EE Server: Presentation Tier; Business Tier           Presentation Tier contains the programming logic for how information is presented to the end user. The presentation tier processes information from the client and business tiers.Business Tier contents the application logic. The business tier processes information from the presentation and data tiers.                                                 Database machine: Data Tier

Why three locations:

easy to maintainquick developmentdevelopers can focus on a particular function.