Computer Science 15-110, Lecture 9 (Sections M-Q), Fall 2009
Lab 3
Due:  Mon 14-Sep-2009 at 11:59pm (email copy to your CA)
(no late submissions accepted).

Read these instructions first!

• The lab instructions from lab2 all apply here.
   
• As explained in that document:
  • Submit your free-response answers in a single file named Lab3.txt (or .doc, .pdf, .rtf, or .html -- but not .docx!).
  • Your top-level directory (which must exist) should be named lab3-<andrewId>.  Submit a zipped version of this.
  • Do not submit .java~ files, .class files, project files, or any other extraneous files.

• Style counts!!!  Use well-named variables, proper indenting, reasonable commenting, etc.
   
• Note:  You may use conditionals ("if" statements or ternary operators (?:)) starting this week!  However, you may not use Java concepts we have not yet covered, including loops (do/while/for), arrays, or methods from any classes in java.util.* (besides Scanner or others we explicitly use) to solve these problems (which isn't a problem for most of you, seeing as we have not yet covered these!). While they may be helpful, every problem here is solvable without them, and they are not permitted for now.

1. Short Answers
2. Tracing
3. Mystery Code
4. Non-Graphics Methods
   1. Rewrite previous problems with conditionals!
5. Animations
   1. Bouncing Ball and Square
   2. BallAroundSquare

1. Short Answers
   There are no short answers in this lab!
    
2. Tracing
   In the written portion of your submission, indicate what each of the following will print or draw  Do not run these programs.  Figure this out by hand.  Remember to show your work.
    

   a)

   public static void main(String[] args) { int u = 11, v = 4; int w = u/v; double x = u/v; double y = 1.0+u/v; double z = 1.0*u/v; System.out.println(w + "," + x + "," + y + "," + z); w += ((u > v) ? u : v); x *= ((u%v > v%u) ? u : v); y /= ((w > x) ? ((x > Math.pow(y,2)) ? 4 : 3) : 2); z = ((z < x) ? (int)(x/z) : (x/z)); System.out.println(w + "," + x + "," + y + "," + z); }

   b)

   public static void main(String[] args) { // Remember: unicode for 'a' is 97 String s = "abcdefg"; int i = (int)Math.sqrt(s.length()); char c = s.charAt(i); boolean b = ((c == 'c') ? (c<100) : (i<c/100)); System.out.println(s + "," + i + "," + c + "," + b); if (s.charAt(s.length()-1) < c) s += s; else if (b == true) s += c; else s += "Go Steelers!"; if ((i >= Math.sqrt(c)) || (b != (s.length() == 0))) i *= 2; else if (i < s.length()) i *= 4; else i *= 8; b = !b; c++; if (c != s.charAt(i)) c++; c++; System.out.println(s + "," + i + "," + c + "," + b); }

    

3. Mystery Code
   In the written portion of your submission, answer the following question in general, and in just a few words of plain English.
    
   1. What does this method do (in general)?
      
      public static boolean f(String s) {
        if ((s == null) || (s.length() > 3))
          return false;
        char c = s.charAt(0);
        char d = ((s.length() == 1) ? c : s.charAt(1));
        char e = ((s.length() == 3) ? s.charAt(2) : d);
        return (c == e);
      }
       
   2. The preceding method contains a bug!  It will crash for one value of s.  Which value of s causes the crash, what is the exact cause of the crash, and what exception is thrown?
       
   3. What does this method do (in general)?

        public static boolean g(int x, int y, int z) {
          if (x < y) {
            int temp = x;
            x = y;
            y = temp;
          }
          if (y >= z)
            return (x == z);
          else if (z >= x)
            return (y == z);
          else
            return (x == y);
        }

   4. What does this program do (in general)?

      import javax.swing.*;
      import java.awt.*;
      
      class MysteryAnimation1 extends JComponentWithEvents {
      
        private int rx = 0;
        private int ry = 0;
        
        public void timerFired() {
          rx = ((rx < getWidth()) ? (rx+20) : 0);
          ry += 20;
        }
      
        public void paint(Graphics2D page) {
          int height = getHeight();
          page.fillRect(rx, height-25-ry%height, 50, 50);
        }
      
        // Standard main method:
        public static void main(String[] args) { launch(300, 300); }
      }

   5. What does this program do (in general)?

      import javax.swing.*;
      import java.awt.*;
      
      class MysteryAnimation2 extends JComponentWithEvents {
        private double t = 0;
        
        public void timerFired()  {
          t += 0.5;
        }
      
        public void paint(Graphics2D page) {
          int cx = getWidth()/2, cy = getHeight()/2;
          int r = 100;
          int x = (int)Math.round(r*Math.cos(t)); // cosine, where t is in radians
          int y = (int)Math.round(r*Math.sin(t)); // sine, where t is in radians
          y = Math.abs(y);
          page.fillOval(cx + x, cy - y, 20, 20);
        }
      
        // Standard main method:
        public static void main(String[] args) { launch(300, 300); }
      }
       

4. Non-Graphics Methods
   First, identify the 2 methods that you wrote for lab1, hw1, lab2, or hw2, that would be particularly clearer or easier or somehow better if written using conditionals rather than with arithmetic.  Choose wisely -- 2 of these methods are especially more difficult without conditions!  Then, in a class named "Lab3" in a file named "Lab3.java", rewrite these methods using conditionals.  At least one of your new methods must use "if" statements, and at least one other must use the ternary operator.  Also, include the test methods you previously wrote to be sure your new versions work properly!
    
5. Animations
   a. Bouncing Ball and Square
   In the file Lab3BouncingBallAndSquare.java, write the animation in this jar file:
      BouncingBallAndSquare.jar  (also available in a zip file:  BouncingBallAndSquare-jarfile.zip)
   Notes:
   • The ball and square move at different speeds.
   • Each bounces as it hits the edges (they do not go even partially past the edges)
   • Each changes color depending on the direction it is moving

   b.  Ball Around Square
   In the file Lab3BallAroundSquare.java, write the animation in this jar file:
      BallAroundSquare.jar (also available in a zip file:  BallAroundSquare-jarfile.zip)
   Notes:

   • The blue box is the largest square you can draw with a 10-pixel margin around it (so you will take the minimum of the width and height when computing the size of the square)
   • The circle pauses on the corners and is red while it pauses.
   • Hint:  the animation itself does not pause when the circle is on the corner -- the timer keeps firing away as normal.  Only your logic must basically ignore the timer for a little while at the right times.  To do this, perhaps you might introduce a counter (maybe called the "pauseCounter") that is set to 0 when you are not paused.  When you want to pause, set the counter to some positive value (say, 10, to start).  Now, when timerFired is called, if your pause counter is positive, just decrement it and return immediately.  Thus, you will ignore some number (again, say 10, to start) of calls to timerFired, and only when the pauseCounter reaches 0 will you again start processing the timer events.
   • Also, you will want to use the page.drawString method to draw the text.  It takes 3 parameters -- a String, and an x and y location at which to draw the string.  The x is the left edge of the string and the y is the "baseline", which is near the bottom of the string.  For example, try this line of code:
        page.drawString("Carpe diem", 50, 100);
     Then, read the online API for the drawString method in the Graphics class for more details.
   • You will also want to use the substring method of the String class.  This method takes 2 parameters -- the starting index (inclusive) and the ending index (exclusive), and returns the substring between them.  For example, "abcdefg".substring(2,5) returns the string "cde".
   • Another hint:  you may want to draw two strings, one per visible line, using different substrings of a third string.

Carpe diem!