COMPROG2
Programming
Language
using JAVA
LESSON 1 – ARRAY (Part 1)
Contents
Basic Concepts
Array Declaration
Array Processing
Parallel Array
Basic Concepts: Array
An array stores values similarly to the
way in which a one-row egg carton
holds eggs.
Sometimes it is advantageous to store
a collection of data together as a unit.
Definition of an Array
An array is a collection of a fixed
number of objects all of the same
type, which are stored sequentially in
computer memory.
The objects in an array are the
array's elements.
We access array elements using their
index or subscript.
Definition of an Array
Definition: An array can hold
multiple values of the same data
type simultaneously.
Steps in declaring array
1. Declare an array reference variable
2. Next step in the process is to use
the new key word to create an array
and assign its address to the
numbers variable.
Declaring an array
Option 1:
Option 2:
Array declaration
The number inside
the brackets is the
array’s size
declarator
 It indicates the number of elements, or
values, the array can hold.
 It is integer type (whole number) ONLY!
numbers = new double[1.5]
 It should be not negative
numbers = new int[-5]
Array declaration
numbers will reference
an array that can hold six elements, each
one an int data type.
Array declaration
Other valid array declaration:
Array declaration
Using a constant variable
Note: This practice can make programs
easier to maintain. When we need to
change the size of the array.
Once an array is created, its size cannot be
changed.
Array initialization
To initialize an array, you use an initialization list
of values separated by commas and enclosed
within curly braces.
Providing values for all the elements in an array
also
is
called
populating
the
array.
Access to Array elements
elements in the array may be accessed and
used as individual variables.
A subscript is used as an index to pinpoint
a specific element within an array.
1st element of array has (0) zero subscript
(always).
Access to Array elements
Subscript numbering always starts at zero.
The last element in array is one less than the
total number of elements in array.
Array [n-1]
Access to Array elements
Subscript numbering always starts at zero.
20
30
Access to Array elements
Subscript numbering always starts at zero.
Assigning values to array:
Displaying array elements
System.out.println(numbers[0]);
System.out.println(numbers[3]);
System.out.println(numbers[1]);
Screen output:
20
30
0
Displaying array elements
Displaying array elements using:
A) For Loop
B) Enhanced For Loop
Displaying array elements
Using For Loop
int[] age = {12, 4, 5};
for(int i = 0; i < 3; i++)
System.out.println(age[i]);
Processing of Array
Array Length
Each array in Java has a public field named length.
This field contains the number of elements in the
array.
Enhanced FOR Loop
Java provides a specialized version of the for loop
that, in many circumstances, simplifies array
processing.
General Syntax:
Enhanced FOR Loop
Java provides a specialized version of the for loop
that, in many circumstances, simplifies array
processing.
General Syntax:
Enhanced FOR Loop
int[] primes = {2, 3, 5, 7, 11};
for (int prime : primes)
{ System.out.println("current number is " + prime);}
Enhanced FOR Loop
When to use enhanced FOR Loop?
When you need to access the values that are
stored in an array, from the first element to the last
element, the enhanced for loop is simpler to use
than the traditional for loop.
Enhanced FOR Loop
Limitations of enhanced FOR Loop
 if you need to change the contents of an array
element
 if you need to work through the array elements in
reverse order
 if you need to access some of the array elements,
but not all of them
 if you need to simultaneously work with two or
more arrays within the loop
 if you need to refer to the subscript number of a
particular element
Displaying array elements
DEMONSTRATION
in JGRASP
Input in array
Scanner keyboard = new Scanner(System.in);
int numbers[]=new int[6];
System.out.println(“Enter value in
numbers[1]”);
numbers[1] = keyboard.nextInt();
Processing of Array using FOR
Processing of Array using FOR
Processing of Array using FOR
CHALLENGE!
Create a program that will ask the number or size of
an array. (To be inputted by the user)
Processing of Array using FOR
CONCEPT
Individual array elements are processed like any
other type of variable.
Parallel Array
In computing, a parallel array is a data structure
for representing arrays of records. Values located
at the same index in each
array are implicitly the fields of the same record.
Parallel Array
Parallel Array
Parallel Array
NOTE:
The true beauty of parallel arrays, is that each
array may be of a different data type.
Parallel Array
DEMONSTRATION in JGRASP
Summary
1. We process array elements thru their subscript
or index.
2. An efficient way to process them is using a
looping control structure (a counter controlled
looping structure) because we know the size
or number of elements.
3. Inputting, displaying and other processing
done in the array and its elements needs
individual looping statements.