LECTURE NOTES
15 NOVEMBER 2004

ARRAYS

Why?
- manipulate a collection of values
- avoid naming each element independently
What?
- *array*: collection of data values of the same type

What?
- declaring an array
How?
  <type>[] <identifier>;
  <type> <identifier>[];
Example?
  int[] testScore;
  float temperature[];

What?
- internal representation of an array
How?
- array itself is a reference data type 
  (draw an array variable and its memory)
- amount of memory allocated to store it varies with the number 
  and type of values in it
- must use reserved word new to allocate this memory

What?
- initializing an array
How?
  <identifier> = new <type>[<size>]
Example?
  temperature = new float[7];
  (draw a picture)

What?
- array is not considered an object

What?
- combine declaration and allocation
Example?
- float temperature = new float[7];

What?
- refering to the collection
How?
- use the array identifier

What?
- *array element*: one of the individual values in an array
- *indexed expression*: expression used to refer to an array element
How?
- zero-based indexing
- biggest index is one less than the number of elements in the array

  <identifier>[<n>]
  - n can be any integer expression
Example
- biggest index in temperature is 6
- if temperature is supposed to represent the temperature of Sunday-Saturday,
  I would refer to Friday's temperature with the expression:
  temperature[5]

Why?
- want to iterate through an array, but don't know size in advance
What?
- determining the size of an array
How?
- public constant member length
Example?
  temperature.length
  - would resolve to 7

What?
- initializing an array (quickly)
- force to do using a loop
How?
- instead of specifying the size of the array, just give a list of initial values
- number of initial values determines the size

  <type>[] <identifier> = {<value 0>, <value 1>, ... , <value n>};

Example?
- if this week's forecast is 34, 42, 44, 43, 45, 47, 33
  float[] temperature = {34f, 42f, 44f, 43f, 45f, 47f, 33f};

Why?
- array size is always the same
  - may not be most efficient use of space
    - if too small, must recompile the program
    - if too large, wasting memory
What?
- *fixed size array declaration*: size of the array is determined at compile time
- *variable-size array declaration*: size of array is determined at run time
How?
- use a variable (or an expression including a variable) to specify the size

STORING OBJECTS IN ARRAYS

What?
- declare an array of objects
How?
- use the name of a class instead of a primitive

  <class name>[] <identifier> = new <class name>[<size];

Example?
  Pet ourPets[] = new Pet[5];

What?
- populating an array of objects
- elements are automatically initialized to null
How?
- each element must also be created

  <identifier>[<index>] = new <class name>();

Example?
  ourPets[0] = new Pet();
  - the array element then points to an object
  - draw a picture

What?
- accessing members and methods of an object in an array
How?
- use indexed expression to refer to the object instead of a variable

  <identifier>[<index>].<method/member>;

Example?
  ourPets[0].setSpecies("cat");