CS115 lecture notes, Spring 1999
Week 8, Monday

Hand back exams and go over them.

QUIZ WEDNESDAY.


Things to review:

1) two types of types

   object types begin with capital letters
   you can invoke methods ON members of object types

   primitive types begin with lower case letters.

2) infinite loops and infinite recursion

3) recursive definitions and recursive methods

   using pseudocode to describe algorithms



The accumulator pattern
-----------------------

Add up a series of terms...

  public static int accumulate (int n) {
    int i = 0;
    int total = 0;

    while (i < n) {
      total = total + (something that depends on i)
      i = i+1;
    }
    return total;
  }


The counter pattern
-------------------

Count how many times something happens...

    String fruit = "banana";
    int count = 0;

    int index = fruit.indexOf ('a');
    while (index != -1) {
      count = count + 1;
      index = fruit.indexOf ('a', index+1);
    }
    System.out.println (count);


In the first example, I "traversed" the integers from 0 to n.
In the second case, I traversed the letters in a String.

But the counting/accumulating pattern is similar in both cases.
In fact, you can think of a counter as a special kind of
accumulator.


Four kinds of methods
---------------------

1) void, fruitful

      (when you invoke a fruitful method, don't forget to
       do something with the result)

2) methods you invoke on objects = Object methods

   methods you just invoke = Class methods

   g.drawOval, System.out.println ...  factorial, paintShirt
                                       Math.cos

   It is probably not clear at this point why Math.cos is
   a class method and System.out.println is an object method.
   That's ok.