Chapter 7

Graphical User Interface

Design in Scheme

In the previous chapters we have been concerned with server side web program 

ming in which the client interacts with the server using a browser. We used

HTML with CSS to create the Graphical User Interface (GUI). The browser

and the server communicate using the HTTP protocol, the responses to the

users input are specified using Scheme.

In this section we consider another approach to web programming in which

the Graphical User Interface is provided by a Scheme program rather than the

browser. The communication is done by sending Scheme expressions back and

forth between clients, and the responses to user input and to communication

input is specified using Scheme.

Web programming, as we discuss in the next few chapters, provides a more

interactive style of programming than is possible with web pages and servlets.

In particular, we will show how to implement chat rooms and instant messaging

programs, along with other type of groupware applications.

7.1

Intro to the JLIB toolkits

We begin with a introduction to a simple toolkit for building graphical user

interfaces (i.e. windows, buttons, menus, etc.) The applets we consider will

pop up one or more windows and allow the user to enter data, press buttons,

connect to databases on the server, chat with other users, etc.

For example, the program in Figure 7.1 is stored in a file  hello.applet 

and if you visit this file with your browser. You will see a page that contains the

five lines of comments describing the program and its author, and your browser

is Java enabled, it will pop up a window with the word  greetings  at the top

in red letters with a Helvetica Bold 60pt font, and a button labelled  goodbye 

beneath. When you click on the button, the window disappears.

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