Java Programming (Arrays)

Single array

A single array variable can reference a large collection of data.

You will have to store a large number of data / values during the execution of a program. Suppose that you need to store 200 numbers to compute their average, sum or find maximum value. So first your computer will read the numbers and should store in variables. Think you have to declare 200 values and repeatedly write almost identical code 200 times huh is it easy? No you will fed-up soon. So how do you solve this problem? Most high level language are provide data structure, the Array, which can store a fixed size collection of elements of the same type.

 

Array – a collection of data or one can think array is a collection of data in same type. Correct.

How to Declare a Array variable?

elementType[] arrayRefVar;

 
The elementType can be any data type, and all elements in the array will have the same data type. For example, the following code declares a variable myList that references an array of double elements.

int[] myList;

  

Creating Arrays

Unlike declarations for primitive data type variables, the declaration of an array variable does not allocate any space in memory for the array. It creates only a storage location for the reference to an array. If a variable does not contain a reference to an array, the value of the variable is null. You cannot assign elements to an array unless it has already been created. After an array variable is declared, you can create an array by using the new operator and assign its reference to the variable with the following syntax:

arrayRefVar = new elementType[length];   

 

elementType[] arrayRefVar = new elementType[arraySize];

or,

elementType arrayRefVar[] = new elementType[arraySize];

Examples of such a statements

char[] myList= new char [10];

To assign values to the element, use the syntax:

arrayRefVar[index] = value;

 

For example, the following code initializes the array.

myList[0] = 34;

myList[1] = 89;

myList[2] = 45;

myList[3] = 23;

myList[4] = 67;

 

This array can illustrate like this

int[] myList= new int[5]

 

myList[0]	34
myList[1]	89
myList[2]	45
myList[3]	23
myList[4]	67

 

Array Initializers Java has a shorthand notation, known as the array initializer, which combines the declaration, creation, and initialization of an array in one statement using the following syntax:

elementType[] arrayRefVar = {value0, value1, ..., valuek};

For example, the statement

double[] myList = {1.9, 2.9, 3.4, 3.5};

declares, creates, and initializes the array myList with four elements, which 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;

In my next post I hope to explain how to process arrays for some purposes.

Thank you guys