Swing Hacks

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Chapter 12, Miscellany

#95 Debug Your GUI

HACK

Notice the odd for loop—you start at the second-to-last element and decre-

ment by two each time. On each pass, you take the first object of the pair; if

it’s the right class to fire the event to, you get the second object of the pair

and call its event-handling method. Presumably, you could use this to mix

up different kinds of listeners in the same list, calling different methods for

different classes.

When run, this test produces the following output. Since the event firing

counts down through the listeners, it’s functionally the same as the simpler

backward

for

loop shown earlier:

[tonberry] cadamson% java EventListenerListEventSource

E called

D called

C called

B called

A called

H A C K

#95

Debug Your GUI Hack #95

Standard out and err aren’t just for log files anymore.

Debugging GUIs often means keeping one or two console windows open, so

you can see the debugging messages you print to standard out (via

System.

out.println( )

and the like), as well as stack traces printed to standard err

when exceptions are caught. In the field, you might want to log these to a

file with something like

java.util.logging, but at design time, or when

investigating a bug, you want to see exactly when the exceptions happen,

and running

tail -f mylog.txt in multiple terminal windows may not be

practical, especially if you’re trying to get a customer on the phone to do it.

An