Chris Pollett>Old Classes>PIC 20, Winter 2000>Hw2

1. For this problem you write an application named Pattern.java. Besides giving you more practice with control structures the point of this exercise is to learn how to do simple pattern matching using finite state automata. This program analyzes its command line arguments to see if the numbers 7, 7, and 9 appear as three successive arguments and then prints an acknowledging response of your choice (go wild) if they do, and a differing response if they don't. Make it clear to enough which response means what so that the grader can grade your homework. Here are some example input response pairs:

   >java Pattern 7 55 7 9 2
   Sorry, doesn't contain the pattern.
   
   >java Pattern 5 4 -79 8 7 7 7 9 0 3
   Yes, that has the pattern.
   
   >java Pattern 0 7 7 9 0 0 0
   Yes, that has the pattern.
   

   You can assume like above that all arguments will be integers. The grader will test on these as well as two other sets of inputs. You should use a break to get out of your loop once you have accepted an input. You should also use a switch/case structure somewhere in your program. To do this assignment it helps to come up with a finite state diagram (will mention in class) which accepts the above kinds of strings and then implement that in java.
2. For this problem you will write an applet named Triangles.java and an html file Triangles.php for appletviewer to view it. The point of this exercise is to get you more familiar with arrays, recursive methods, simple use of the Java event model, and to see a simple example of self-similarity ( a fractal). Your goal is to write a program which does the same thing as the applet below.

• The triangles above should be drawn using the drawPolygon(int x[], int y[], numberOfPts) method of the class Graphics. The first array x[] specifies each x coordinate of points in the polygon. The second array y[] specifies each y coordinate of points in the polygon. numberOfPts says the total number of points in the polygon. i.e., 3 for a triangle. For this problem you should write a recursive method in your applet called:

  
  void drawTri(int xPts[], int yPts[], Graphics g, int nest)
  

  which is called by the paint method after a button click and a nesting depth has been entered. If nest >=1 , this method calls g.drawPolygon(xPts, yPts,3); to print a triangle. Then by finding the midpoints of each edge in this triangle it makes three new triangles and calls drawTri on these three new three new triangles but on a one smaller value of nest. Self-similarity just means that if you could continue the nesting of triangles to infinity that each subtriangle would look like a copy of the whole triangle. The coordinates of your outermost triangle only need to be roughly the same as mine.

Homework 2 FAQ.

Solution set.