Introduction To Practical Computer Science I - Lec 12 (Arrays).pptx

Introduction To Practical Computer Science I
Lecture 12: Arrays
Herat University
Computer Science Faculty
Lecturer: Abdul Khaleq Herawi
Date: 2024

2
Outline:
 Creating and initializing arrays
 IndexedVariables
 Array Initializers
 Array Initialization using shorthand notation

INTRODUCTIONTO JAVA PROGRAMMING (10TH ED.)Y. DANIEL LIANG 3
OPENING PROBLEM
Read one hundred numbers, compute their average, and find out how many numbers are
above the average.

Introducing Arrays
Array is a data structure that represents a collection of the same types of data.
5.6
4.5
3.3
13.2
4
34.33
34
45.45
99.993
11123
double[] myList = new double[10];
myList reference
myList[0]
myList[1]
myList[2]
myList[3]
myList[4]
myList[5]
myList[6]
myList[7]
myList[8]
myList[9]
Element value
Array reference
variable
Array element at
index 5

Declaring ArrayVariables
 datatype[] arrayRefvar;
 example:
double[] mylist;
 datatype arrayRefvar[]; / / this style is allowed, but not preferred
 example:
double mylist[];

Creating Arrays
arrayRefvar = new datatype[arraysize];
example:
mylist = new double[10];
mylist[0] references the first element in the array.
mylist[9] references the last element in the array.

DECLARING AND CREATING IN ONE STEP
datatype[] arrayrefvar = new datatype[arraysize];
double[] mylist = new double[10];

The Length of an Array
Once an array is created, its size is fixed. It cannot be changed. You can find its size using
 arrayRefvar.length
For example,
 Mylist.length returns 10

DEFAULTVALUES
When an array is created, its elements are assigned the default value of
 0 for the numeric primitive data types,
 'u0000' for char types, and
 false for boolean types.

IndexedVariables
 The array elements are accessed through the index. The array indices are 0-based, i.e., It
starts from 0 to arrayrefvar.length-1.
 Each element in the array is represented using the following syntax, known as an indexed variable:
 arrayRefvar[index];

Using IndexedVariables
After an array is created, an indexed variable can be used in the same way as a regular
variable. For example, the following code adds the value in mylist[0] and mylist[1] to
mylist[2].
 mylist[2] = mylist[0] + mylist[1];

Array Initializers
 Declaring, creating, initializing in one step:
double[] mylist = {1.9, 2.9, 3.4, 3.5};
This shorthand syntax must be in one statement.

Declaring, creating, and initializing using the shorthand notation
double[] mylist = {1.9, 2.9, 3.4, 3.5};
This shorthand notation is equivalent to the following statements:
double[] mylist = new double[4];
 mylist[0] = 1.9;
 mylist[1] = 2.9;
 mylist[2] = 3.4;
 mylist[3] = 3.5;

Caution!
Using the shorthand notation, you have to declare, create, and initialize the array all in one statement. Splitting it would
cause a syntax error. For example, the following is wrong:
double[] mylist;
mylist = {1.9, 2.9, 3.4, 3.5};

Introduction To Practical Computer Science I - Lec 12 (Arrays).pptx

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