CS 5JA, Winter 2009
Assignment 4 - More control structures, including nested loops

Due: Tuesday, February 24, 9:00 pm
Worth: 100 homework points

1. Write OvalDrawing.java to complete a modified version of the graphical application specified in the "GUI and Graphics Case Study" Exercise 5.1 on page 194 of the text.
   • Key changes from the text exercise:
     • Draw ovals, not circles (i.e., width and height can vary).
     • Draw a variable number of them, not just always 12.
     • Fill the window as described below, not just draw fixed sizes and spacing.
   • The class must extend JPanel like class Shapes (Fig. 5.26) on page 192.
   • Include an instance variable to store the number of ovals to be drawn.
   • Include a constructor that takes one int parameter, and sets the value of the instance variable to the value of this parameter.
   • Write the method, public void paintComponent(Graphics g) to draw the specified number of ovals as concentric rings. All ovals should be centered in the panel. The smallest oval should have width and height equal to getWidth() and getHeight(), respectively divided by the total number of ovals. The largest oval should touch the edges of the window, and remaining ovals should be equally spaced between these two extremes.
     Hint: Calculations should be done with double values for accuracy, and results converted to int for passing to the drawOval() method.
   • Use OvalDrawingTest.java to test your class. (Notice the way it handles user input too, as you will need to apply such techniques in part 2.)
   • Here are sample results for 6 and 50 ovals at original size. Here are the effects of a user stretching 20 wider and 50 taller.
2. Write a modified version of the Java application specified in Exercise 5.22 on page 202 of the text (also see the instructions, examples and hint of Exercise 5.15 on pp. 200-201).
   • TrianglePrinting.java must be the application's name.
   • Key changes/clarifications from the text exercise:
     • The user specifies the number of rows (i.e., triangle size) to print.
     • The user specifies the character used to print the triangles.
     • One blank space separates each pair of triangles.
     • The user's input is checked for errors, and the user may re-enter data if an error is made.
   • In this example, the user requests 5 rows of plus signs (the user's input is shown in blue):

             Enter triangle size: 5
             Enter character: +
             +     +++++ +++++     +
             ++    ++++   ++++    ++
             +++   +++     +++   +++
             ++++  ++       ++  ++++
             +++++ +         + +++++

   • Do not allow the user to enter a size of less than 1, and do not let the program crash if the user enters a string that is not an integer. Here is a longer set of runs from our solution - notice the input error checking. Your results should exactly match these results.
   • To retrieve the character entered by the user (e.g., + in the example above) as a char, use the String method charAt(0) to extract the first character of the user's input:
     
     input.next().charAt(0) // gets first char from Scanner object named input

     More hints - you might want to think about the problem and solve it as if it consists of four parts, one for each triangle. The leftmost triangle is the simplest to print (nested for loops work well). You could get that part working first, then modify the program to add the second triangle, and so on. Notice the first and second triangles both require spaces after the characters to fill their rectangular regions, just like the third and fourth triangles require such spaces before the characters.
3. Turn in OvalDrawing.java and TrianglePrinting.java here before the deadline.

Updated 2/10/09, by C. Michael Costanzo