LECTURE NOTES
NOVEMBER 17 2004

ASSIGNMENTS
Fri 11/19 CodeLab #11
Mon 11/22 Assignment #4

ORGANIZING ARRAYS

What?
- organizing an array
How?
- (1) all non-null elements before all null elements
- (2) null elements interspersed among non-null elements

What?
- removing an object from an array (1)
How?
- set that element to null

What?
- removing an object from an array (2)
How?
- (a) swap last real element and deleted element
  - good if unsorted
- (b) move all elements over one
  - good if need to maintain some kind of order

Exercise:
- write some code to insert into ourPets
- write some code to search ourPets
- write some code to delete from ourPets
- discuss: pros and cons of organization that we chose

USING ARRAYS WITH METHODS

Why?
- arrays are reference variables
What?
- treat an array like an object with respect to methods

What?
- declaring an array as a parameter
How?
  <method name>(<type>[] <identifier>) {}
  <method name>(<type> <identifier>[]) {}
Example?
  public double getMin(double[] temps) {}
  public boolean exists(int element, int collection[]) {}

What?
- passing an array as a parameter
Example?
  int[] myInts = {5, 8, 23, 1, 4};
  boolean contains23 = exists(23, myInts);

What?
- returning (a reference to) an array from a method
How?
  <type>[] <method>() {}
Example?
  int[] fibonacci(int numTerms) {}

What?
- using an array returned from a method
Example?
  int[] fibonacci3 = fibonacci(3);
  for (int i = 0; i < fibonaaci3.length; i++) {
      System.out.println(fibonnaci3[i]);
  }

What?
- since an array is a reference, an array passed as a parameter can be modified by a method
- using a method to modify an array
- draw a picture
Example?
  void incrementEach(char[] input) {
      for (int i = 0; i < input.length; i++) {
          input[i] += 1;
      }
  }

  public static void main( String[] args ) {
      char[] myName = {'M', 'i', 'c', 'h', 'e', 'l', 'l', 'e'};
      incrementEach(myName);
      for (int i = 0; i < myName.length; i++) {
          System.out.print(myName[i]);
      }
  }

STRETCHY ARRAYS

Why?
- even the user doesn't always know the size of the array
- want to make arrays that automatically grow if necessary
What?
- stretchy arrays
How?
- create a class
- have an add method that grows the array if there'sno more room
  - allocate a bigger array
    - typically new size is between 125% and 200% of the original size
      - don't want to waste too much memory
      - also don't want to have to grow too often
  - copy the data over
  - point the class data to the bigger array
  - the smaller array will automatically be cleaned up