Smalltalk and Object Orientation: an Introduction - Free

4.5.2.2 System Transcript
The System Transcript is a text window which has the additional property of supporting display
operations from expressions as they are executed. It can be referred to using the name Transcript. In
effect, it is the output window of the VisualWorks system. It is where the system itself reports
important information such as when the image was last saved etc.
It is also very useful as a quick way of outputting information, for example by placin g trace
statements within code to see exactly what is happening or for displaying the results of computations
which do not require sophisticated presentation. For example:
Transcript show: 'John'.
You can do this anywhere within any part of your code because Transcript is actually a global
variable and an instance of a class called TextCollector. The Transcript (and other
TextCollectors) respond to the message:
show aString
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Other useful messages understood by the Transcript include: cr ( starts a new line in the
Transcript.), space (puts a single space in the Transcript) and tab (puts a ‘tab’ in the Transcript).
The Transcript only knows how to print strings. Therefore, to make it easy to print anything in the
Transcript, you can use a me ssage called printString. All objects understand this message (as it is
implemented in the class Object). When sent to an object, the result is a printable string which
represents the object. The result will be different depending on th e class of the object, but you are
guaranteed something you can print. The way to use printString is:
Transcript show: someObject printString
Type the following into the Workspace (this is the window at the bottom right of Figure 4.3, more
information on this window is provided in the next chapter). Once you have typed it in, select it with the
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left mouse button. Now use the right mouse button to bring up the window menu . This menu has a
number of options on it, half way down you will see an option called do it. Select this option. The code
will then be executed and the results will be printed in the Transcript.
Transcript show: 'Hello World'.
Transcript show: (3 + 4) printString.
Transcript cr.
You have now written your first piece of Smalltalk. This illustrates an important point, that with
Smalltalk you will get the most out of any book or course by trying things out. So try things out;
explore, be adventurous; it is the quickest way that you will learn.
4.5.3 The System Browser
The System Browser allows the user to inspect the definition of any object in the system, and to modify
it if required. More than one browser can be displayed simultaneously (indeed it is oft en useful to have
a number of browsers open at the same time so that different classes can be considered at the same
time).
The System Browser is made up of five subviews (or windows) and two complementary items
marked instance and class. By default, the instance item is selected; this means that the messages
displayed are the ones sent to instances of a class rather than to the class itself. Note that each of the
subviews has an independent scroll bar. The System Browser is illustrated in the middle of Figure 4.3.
In the figure, the object class has been selected (this is indicated in the second window across the top).
From left to right, the top four panes in the System Browser are :
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This is an example of Smalltalk terminology. Rather than say that some procedure has been defined for a n object, Smalltalkers
say that it understands it.
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This assumes that you are using a two button mouse, for example on a PC. If your mouse has only one button please refer to
the VisualWorks system manuals to find out what the appropriate key sequence is to mimic the second and / or third mouse
button. If you have a three button mouse then the middle button is the equivalent of the right button on a two button mouse.
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