Computer Science 15-100 (Sections T & U), Spring 2008
Class Notes:  Ch 4+5:  Classes, Methods, Conditionals, and Loops (1 of 3)

Logistics

1. Schedule
   1. Hw4 due tomorrow
      Tonight's office hours to be announced in today's class
   2. Quiz 4 on Tuesday (does not cover today's material)
2. Reading:
   1. L&L Chapter 4:  Writing Classes
           Section 4.4 today:  Anatomy of a Method
   2. L&L Chapter 5:  Conditionals and Loops
           Sections 5.1, 5.2, parts of 5.8 today

Topic Outline:

On the Merits of Attending Recitation

Methods, Conditionals, and Loops (Oh my!)

1. Writing Static Methods
   
   a) void methods with no parameters
   
   class MyCode {
      public static void doSomething() {
         System.out.println("Carpe diem");
      }
   
      public static void main(String[] args) {
         doSomething();
         doSomething();
      }
   }
   
   b) void methods with one parameter
   
   class MyCode {
      public static void printSquare(int n) {
         System.out.println(n + "^2 = " + (n*n));
      }
   
      public static void main(String[] args) {
         printSquare(2);
         printSquare(3);
      }
   }
   
   c) void methods with multiple parameters
   
   class MyCode {
      public static void printPower(double base, double exponent) {
         System.out.println(base + "^" + exponent + " = " +
                            Math.pow(base,exponent));
      }
   
      public static void main(String[] args) {
         printPower(2,3);
         printPower(2,0.5); // square root!
      }
   }
   
   d) int methods (Methods that Return Values)
   
   class MyCode {
      public static int getSquare(int n) {
         return n*n;
      }
   
      public static void main(String[] args) {
         int n, nSquared;
         n = 3;
         nSquared = getSquare(n);
         System.out.println(n + "^2 = " + nSquared);
         n = 4;
         nSquared = getSquare(n);
         System.out.println(n + "^2 = " + nSquared);
      }
   }
   
   e) Methods can call other methods:
   
   class MyCode {
      public static int getSquare(int n) {
         return n*n;
      }
   
      public static void printSquare(int n) {
         System.out.println(n + "^2 = " + getSquare(n));
      }
   
      public static void main(String[] args) {
         printSquare(3);
         printSquare(4);
      }
   }
   
   f) Can also have methods return double, char, String, boolean, or any other type!
   
   class MyCode {
      public static double getCubeRoot(double d) {
         return Math.pow(d,1.0/3.0);
      }
   
      public static void printCubeRoot(double d) {
         System.out.println(d + "^(1/3) = " + getCubeRoot(d));
      }
   
      public static void main(String[] args) {
         printCubeRoot(8);
         printCubeRoot(9);
      }
   }
   
   g) Local variables
   Aside:  Methods can have local variables (just like main):
   
   h) Parameters are local variables!
   
   i) Local variables are local -- they only exist within the method where they are defined!
   Aside:  this means different methods can have local variables with the same name, but these are different variables.
    
2. Simple "for" Loops
   
   a)  Print the numbers from 1 to 5:
   
   int x;
   for (x=0; x<=5; x++) {
      System.out.println("x = " + x);
   }
   
   b)  Print the SUM of the numbers from 1 to 5:
   
   int x;
   int sum = 0;
   for (x=0; x<=5; x++) {
      System.out.println("x = " + x);
      sum += x;
   }
   System.out.println("sum = " + sum);
    
3. Simple "if" statements
   
   a)  Print the sum of the ODD numbers from 1 to 5:
   
   int x;
   int sum = 0;
   for (x=0; x<=5; x++) {
      if (x % 2 == 1) {
         System.out.println("x = " + x);
         sum += x;
      }
   }
   System.out.println("sum = " + sum);
    
4. Putting it together:  Using Methods, Conditionals, and Loops:  isPrime and nthPrime!