Lecture 3 Arrays on object oriented programming language

Course: Object Oriented Programming (CS F213)
20/01/25
Prof. Anita Agrawal,
BITS-Pilani-K.K. Birla Goa campus
LECTURE 3A
ARRAYS
1

ARRAYS
❖An array holds a fixed number of values of a single
type.
❖It allows to store and access large number of values
conveniently.
❖Syntax:
datatype[] identifier;
❖ Example: int [ ] age;
❖ Alternate form: int age [];
2
Anita Agrawal (CS F213)

❖ dataType can be a primitive data type like: int, char, byte
etc. or an object.
❖ Identifier (variable name) can be anything provided that it
follows the rules and conventions of identifiers.
❖ int [ ] age; [value of age is null]
does not actually create an array;
3

CREATING THE ARRAY
 To create an array, use the new operator.
 Syntax: var-name = new type[size];
▪ Example: age = new int [5];
allocates memory for 5 integer elements and assigns the array
to the age variable.
▪ Default value: 0 for numeric
▪ false for boolean, etc..
4

ALTERNATE WAY
int [] age;
age = new int [5]; int[] age = new int[5];
Imp: Once the length of the array is defined, it cannot
be changed in the program.
5

ACCESSING THE ARRAY
❖In case of primitive data types, the actual values
are stored in contiguous memory locations.
❖Each element is accessed by its numerical index.
❖Numbering begins with 0.
❖The 5th element, for example, would therefore be accessed at index 4.
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INITIALISING THE ARRAY
 int[] age = new int[5];
 age [0] = 10; // initialize first element
 age [1] = 5; // initialize second element
 age [2] = 30; // and so forth
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ALTERNATE SYNTAX
 Shortcut syntax to create and initialize an array:
▪ int[ ] age = { 10, 5, 30, 25,40 };
 Here the length of the array is determined by the number of
values provided between braces and separated by commas.
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EXAMPLE
Write a main method to initialise an array ‘age’
with the values 1,5,2,7,8 and display the values
on the console in the form:
Element at index 0: 1
:
:
:
.
9
ArrayExample.java

OUTPUT
 Element at index 0: 1
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EXAMPLE 2
Write a main method to declare an array ‘age’of
5 elements and initialise the values of the 1st
and 3rd element with 34 and 14 respectively.
Display the values of all the elements on the
console in the form:
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ArrayExample.java

OUTPUT OF THE PROGRAM
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MULTIDIMENSIONAL ARRAYS
 An array of arrays/multidimensional array.
 An array whose components are themselves arrays, unlike
C or Fortran.
 The rows are allowed to vary in length.
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Right index:
column
Left index:
row
Anita Agrawal (CS F213) 14

MULTIDIMENSIONAL ARRAYS (CONTD…)
Example:
String[][] names = { {"Mr. ", "Mrs. ", "Ms. "},
{“X", “Y"} }
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Print:
Mr. X
Ms. Y
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 For a multidimensional array, we only need to specify the
size for the first (leftmost) dimension
 int [][] twoD = new int[4][];
 twoD[0] = new int[5];
 Also possible to write: twoD[0]={10,6,12,13,5};
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 No need to allocate the same number of elements
for each dimension
 int twoD[][] = new int[4][];
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twoD.java

ALTERNATE DECLARATION
int[] a1, a2, a3;
or
int a1[], a2[], a3[];
Next……classes and objects
19

Lecture 3 Arrays on object oriented programming language

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