82 CHAPTER 7. GRAPHICAL USER INTERFACE DESIGN IN SCHEME

"Greeting"

"Tim Hickey"

"http://www.cs.brandeis.edu/~tim"

"This pops up a greeting window"

"http://www.cs.brandeis.edu/~tim/hickey.new.gif"

(jlib.JLIB.load)

(define win

(window "hello"

(col

(label "Greetings"

red

(HelveticaBold 60)

(button

"goodbye"

(action (lambda(e) (.hide win))))))))

(.pack win)

(.show win)

Figure 7.1: hello.applet

If you change the filename from hello.applet to hello.snlp, and if you

have installed the Java Web Start plug in

1

then the browser will download the

program as a Java Web Start application and it will again pop up a window as

before. The difference with Java Web Start is that the next time you visit that

link, the browser will only download the program if there has been a change in

the code. If not, then it will use the version it has stored on your disk. Moreover,

you can disconnect your computer from the net and still run the stored copy of

the program.

The program if Figure 7.1 illustrates a number of features of the JLIB toolkit.

First, observe that it defines three components:

  a label

  a button, and

  a window.

Each of these components has a string written somewhere on it ( Greetings ,

 goodbye , and  hello  respectively). The label has also been given a specified

color and font, and the button has been given an action. The relative position

of the label and button has been specified by the col layout procedure, which

states that the label and button should appear in a column. Finally, the

action on the button causes the window to disappear when the button is

pushed. The last two commands are (.pack win) which does the window layout

1

http://java.sun.com/products/javawebstart