1. CSCI 3333 Data Structures Array
by Dr. Bun Yue Professor of Computer Science

2. What is an array?
Wikipedia’s array data structure: “a data structure consisting of a collection of elements (values or variables), each identified by at least one array index or key.”
Array in Wikipedia:
There are many definitions.

3. Array Definitions
Many kinds and definitions of arrays: arrays, association arrays, array data types, array classes, …
E.g.
Java: “An array is a container object that holds a fixed number of values of a single type.”

4. Array definitions
C++: “An array is a series of elements of the same type placed in contiguous memory locations that can be individually referenced by adding an index to a unique identifier.”
Perl: “An array is an ordered sequence of scalars.”

5. Array Essential concepts: A container Ordered
Elements of identical types
Element identified by indices

6. Differences Among Languages
C++: int a[] = {2,4,6,8};
Java & C#: int[] a= {2,4,6,8};
= {2,4,6,8};
PHP: hash and array the same
$a=array(2,4,6,8);
$b=array(‘bun’=>2, ‘ben’=>4);
JavaScript: object
var a=new Array(2,4,6,8);

7. Arrays in various languages
Java
C++
Perl
PHP
Javascript
Nature
Built-in
Built-in; map
Object
Element Size
Fixed
Variable
# elements
Element Type
Any
Scalar
Pointer (Arithmetic) No
Yes
Mainly no
Index/key
Non-negative integer
Integer
Integer or string
non-negative integer

8. Arrays in Java Java has: Built-in array construct
Classes and Interfaces associated with array.

9. Java’s arrays Zero-based Fixed size Elements have the same type.
An array variable is a handle (reference) to an array.

10. RandomNumbers.java
As an example, we study the program RandomNumbers.java here.
Code reading: what does the code to?
Any conclusion in running the program?

11. Copying array
To copy all element values of b to a (assuming a and b have the same size), this is incorrect:
int[] a = new int[]{1,2,3,4,5};
int[] b = new int[5];
a=b;
// a and b refer to the same array.
// the initial array referred by a becomes garbage.

12. Array cop Instead, use: for(int i=0; i<5; i++) { a[i]=b[i]; } or
System.arraycopy(b, 0, a, 0, 5);

13. Questions and Comments?