Computer Science 15-100 (Sections T & U), Fall 2007
Class Notes, Day 4:   Thu 6-Sep-2007

Logistics

1. Schedule
   • Hw1 due today (deadline = 3:05pm sharp)
   • Hw2 will be posted tonight.  It is due one week from today.
   • Recitation tomorrow:  review hw1 solutions + help on hw2
   • Quiz1 on Tuesday (next class!):covers material through hw1, including all the reading and class notes
2. Reading
   • L&L Chapter 2:  Data and Expressions
     Sections 2.3 - 2.5, 2.7 - 2.9 for Thursday

Topic Outline:

1. Different-sized integers

   public class MyCode {
      public static void main(String[] args) {
         // Demonstrate the different integer primitive data types
         long  xlMax = Long.MAX_VALUE;
         int   xiMax = Integer.MAX_VALUE;
         short xsMax = Short.MAX_VALUE;
         char  xcMax = Character.MAX_VALUE;
         byte  xbMax = Byte.MAX_VALUE;
   
         long  xlMin = Long.MIN_VALUE;
         int   xiMin = Integer.MIN_VALUE;
         short xsMin = Short.MIN_VALUE;
         char  xcMin = Character.MIN_VALUE;
         byte  xbMin = Byte.MIN_VALUE;
   
         // Note:  you do not yet need to know about "printf" (soon...)
         System.out.printf("%5s %25s %25s\n","type","max","min");
         System.out.printf("%5s %25d %25d\n","long", xlMax,xlMin);
         System.out.printf("%5s %25d %25d\n","int",  xiMax,xiMin);
         System.out.printf("%5s %25d %25d\n","short",xsMax,xsMin);
         System.out.printf("%5s %25d %25d\n","char", (int)xcMax, (int)xcMin);
         System.out.printf("%5s %25d %25d\n","byte", xbMax,xbMin);
      }
   }

2. Floating-point numbers

   public class MyCode {
      public static void main(String[] args) {
         // Demonstrate the different integer primitive data types
         float  xfMax = Float.MAX_VALUE;
         double xdMax = Double.MAX_VALUE;
   
         float  xfMin = Float.MIN_VALUE;  // Not what you may expect!!!
         double xdMin = Double.MIN_VALUE;
   
         // Note:  you do not yet need to know about "printf" (soon...)
         System.out.printf("%5s %25s %25s\n","type","max","min");
         System.out.printf("%5s %25g %25g\n","float",  xfMax,xfMin);
         System.out.printf("%5s %25g %25g\n","double", xdMax,xdMin);
      }
   }

3. Characters

   class MyCode {
     public static void main(String[] args) {
       char c1 = 'A';
       char c2 = (char)66;
       char c3 = "ABCD".charAt(2);
       System.out.println("c1 = '" + c1 + "'");
       System.out.println("c2 = '" + c2 + "'");
       System.out.println("c3 = '" + c3 + "'");
     }
   }

4. Booleans

   class MyCode {
     public static void main(String[] args) {
        boolean b1 = true;
        boolean b2 = false;
        boolean b3 = (b1 && b2);  // b1 AND b2
        boolean b4 = (b1 || b2);  // b1 OR b2
        boolean b5 = !b1;         // NOT b1
        System.out.println("b1 = " + b1);
        System.out.println("b2 = " + b2);
        System.out.println("b3 = " + b3);
        System.out.println("b4 = " + b4);
        System.out.println("b5 = " + b5);
    }
   }

5. integer vs floating-point division

   class MyCode {
     public static void main(String[] args) {
       int i = 10;
       double d = 10;
       System.out.println( 10 / 3 );
       System.out.println(  i / 3 );
       System.out.println(  d / 3 );
       System.out.println( 10 / 3.0 );
       System.out.println(  i / 3.0 );
     }
   }

6. Approximate values of floating-point numbers

   class MyCode {
     public static void main(String[] args) {
       double d1 = (29 / 7.0) * 7.0;
       double d2 = 29;
       System.out.println(d1 == d2);
       System.out.println(d2 - d1);
     }
   }

7. Operator Precedence and Association

   See Figure 2.4 (p. 78)
    

8. Increment and Decrement Operators

   a)  As Statements

   class MyCode {
     public static void main(String[] args) {
       int x = 5;
       System.out.println(x); // 5
       x++;
       System.out.println(x); // 6
       ++x;
       System.out.println(x); // 7
       x--;
       System.out.println(x); // 6
       --x;
       System.out.println(x); // 5
     }
   }

   b)  As Expressions

   class MyCode {
     public static void main(String[] args) {
       int x = 5, y = 0;
       System.out.println(x + "," + y); // 5,0
       y = x++;
       System.out.println(x + "," + y); // 6,5
       y = ++x;
       System.out.println(x + "," + y); // 7,7
       y = 10 + x--;
       System.out.println(x + "," + y); // 6,17
       y = 10 + --x;
       System.out.println(x + "," + y); // 5,15
     }
   }

9. Assignment Operators

   class MyCode {
     public static void main(String[] args) {
       int x = 5;
       System.out.println(x); // 5
       x += 2;
       System.out.println(x); // 7
       x *= 2;
       System.out.println(x); // 14
       x %= 9;
       System.out.println(x); // 5
       x /= 2;
       System.out.println(x); // 2
       x -= 5;
       System.out.println(x); // -3
     }
   }

10. Data Conversion

    a)  Widening (automatic) versus Narrowing (manual, lossy)

    b)  Assignment Conversion

    class MyCode {
      public static void main(String[] args) {
         int a = 5;
         double b = a; // Assignment conversion!  
         System.out.println("a = " + a); // 5
         System.out.println("b = " + b); // 5.0
      }
    }

    c)  Promotion

    class MyCode {
      public static void main(String[] args) {
         int a = 5;
         double b = (2.0 + a); // Promotion!  
         System.out.println("a = " + a); // 5
         System.out.println("b = " + b); // 7.0
      }
    }

    c)  Casting

    class MyCode {
      public static void main(String[] args) {
         double a = 5.0;
         int b    = a; // Will not compile!
         System.out.println("a = " + a);
         System.out.println("b = " + b);
      }
    }

    So we cast the double into an int:

    class MyCode {
      public static void main(String[] args) {
         double a = 5.0;
         int b    = (int) a; // Casting!
         System.out.println("a = " + a); // 5.0
         System.out.println("b = " + b); // 5
      }
    }

    Note that casting truncates:

    class MyCode {
      public static void main(String[] args) {
         int a = (int)5.9;
         int b = (int)-5.9;
         System.out.println("a = " + a); // 5
         System.out.println("b = " + b); // -5
      }
    }

11. More on the Scanner

    a)  From p. 87:  Just need to know the methods next***()
    next(), nextLine(), nextBoolean(), nextByte(), etc...

    b)  next() versus nextLine()
    
    Does not work quite as you might expect:
      * next returns next input token as a String
      * nextLine returns the rest of the current line as a String
      * they do not mix-and-match well!

    class MyCode {
      public static java.util.Scanner scanner = new java.util.Scanner(System.in);
      public static void main(String[] args) {
         String s1, s2;
         System.out.print("Enter a few words: ");
         s1 = scanner.next();
         System.out.print("Enter a few other words: ");
         s2 = scanner.nextLine();
         System.out.println("s1 = '" + s1 + "'");
         System.out.println("s2 = '" + s2 + "'");
      }
    }

    Do this again, but just use next, not nextLine:

    class MyCode {
      public static java.util.Scanner scanner = new java.util.Scanner(System.in);
      public static void main(String[] args) {
         String s1, s2, s3;
         System.out.print("Enter a few words: ");
         s1 = scanner.next();
         s2 = scanner.next();
         s3 = scanner.next();
         System.out.println("s1 = '" + s1 + "'");
         System.out.println("s2 = '" + s2 + "'");
         System.out.println("s3 = '" + s3 + "'");
      }
    }
    

    Once more, but just use nextLine, not next:

    class MyCode {
      public static java.util.Scanner scanner = new java.util.Scanner(System.in);
      public static void main(String[] args) {
         String s1, s2;
         System.out.print("Enter a few words: ");
         s1 = scanner.nextLine();
         System.out.print("Enter a few other words: ");
         s2 = scanner.nextLine();
         System.out.println("s1 = '" + s1 + "'");
         System.out.println("s2 = '" + s2 + "'");
      }
    }

12. Graphics (quickly -- more next time!)
    
    a)  Applet  vs  Application
    
    b)  Writing graphics code in an Application:
    

    import javax.swing.*;
    import java.awt.*;
    
    public class Test extends JComponent {
       public  static void main(String[] args) {
          runApplication(new Test());  // change "Test" to the name of your class!
       }
    
       public void paint (Graphics page) {
          final int MID = 150;
          final int TOP = 50;
          
          // setBackground(Color.cyan);
          page.setColor(Color.cyan);
          page.fillRect(0,0,getWidth(),getHeight());
          
          page.setColor (Color.blue);
          page.fillRect (0, 175, 300, 50);  // ground
          
          page.setColor (Color.yellow);
          page.fillOval (-40, -40, 80, 80);  // sun
          
          page.setColor (Color.white);
          page.fillOval (MID-20, TOP, 40, 40);      // head
          page.fillOval (MID-35, TOP+35, 70, 50);   // upper torso
          page.fillOval (MID-50, TOP+80, 100, 60);  // lower torso
          
          page.setColor (Color.black);
          page.fillOval (MID-10, TOP+10, 5, 5);   // left eye
          page.fillOval (MID+5, TOP+10, 5, 5);    // right eye
          
          page.drawArc (MID-10, TOP+20, 20, 10, 190, 160);   // smile
          
          page.drawLine (MID-25, TOP+60, MID-50, TOP+40);  // left arm
          page.drawLine (MID+25, TOP+60, MID+55, TOP+60);  // right arm
          
          page.drawLine (MID-20, TOP+5, MID+20, TOP+5);  // brim of hat
          page.fillRect (MID-15, TOP-20, 30, 25);        // top of hat
       }
       
       public static void runApplication(JComponent component) {
          component.setOpaque(true);
          JFrame frame = new JFrame(component.getClass().getName());
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.getContentPane().setLayout(new BorderLayout());
          frame.getContentPane().add(component);
          frame.getContentPane().setBackground(Color.white);
          frame.setSize(300,300);
          frame.setVisible(true);
       }
    }

Carpe diem!