CSC 172
Homework assignment 5

Assigned 8 Apr, 1999
Due 20 Apr, 1999

An Applet with GUI Components and Fonts

Version 1

Write an applet that shows a TextField big enough for 40 characters (on the top line); four buttons labelled "print", "println", "clear", and "quit" (in a row below the TextField), and a TextCanvas occupying the rest of the window. "TextCanvas" is not a predefined class; it's a class you need to define, as a subclass of Canvas. For this version, you only need to get it to show up on the screen, which requires that you write a constructor for it containing the line

setBackground (Color.white);

For the moment, it doesn't need to do anything else. The buttons, likewise, don't need to do anything yet except show up on the screen. At right is my solution.

Hint: If you start working on this and don't see a white rectangle occupying the bottom part of your window, it's probably because your TextCanvas has no size. If it's added to the North, South, or Center part of a BorderLayout, it'll automatically be stretched horizontally to the full width of the window. If it's added to the East, West, or Center part, it'll automatically be stretched vertically to whatever space is left between the North and South parts. So if you want it to be stretched in both directions, you need to figure out how to make it the Center part of a BorderLayout.

Version 2

Add a public "paint()" method to your TextCanvas class that draws several strings in several different places.

Version 3

Add three public methods named "print", "println", and "clear" to your TextCanvas class. "print" and "println" should each take a String parameter and print it within the TypingCanvas. The catch is, the TypingCanvas needs to remember where each string ended, so it can start the next one just to the right of it (or, if it was printed using "println", at the left-hand margin on the next line).

To test this, add the following lines (or something similar) to the "paint()" method you wrote in Version 2.

print ("Hello ");
println ("there.  This should be on the same line.");
println ("But this should be below it,");
print ("while this is on yet a third line.");

Note: When I first wrote this assignment, I suggested putting these lines into the "init()" method of the Applet. That doesn't work, because during the "init()" method, the TypingCanvas doesn't have a Graphics context yet so it can't draw any strings in its Graphics context. This version, however, works.

Version 4

The obvious Version 4 is to make the buttons work. To wit, when the user presses the "print" button, whatever text is in the TextField should be "print"ed. When the user presses the "println" button, whatever text is in the TextField should be "println"ed (i.e. the next thing to be printed will be at the left edge of the next line). When the user presses the "clear" button, the TypingCanvas will be cleared, and the next thing to be printed will be at the upper left hand corner of the TypingCanvas. And when the user presses the "quit" button, the applet ends.

Since I've only posted version 4 on April 15, it's obviously not due April 15. Work on it as soon as you've finished the previous versions.

My version should be in the right-hand margin, but it doesn't seem to run; I'm still trying to figure out why.

Last modified: Thu Apr 15 10:16:02 EDT 1999

Stephen Bloch / sbloch@adelphi.edu

CSC 172 Homework assignment 5