Java Programming/Arrays

About Arrays

An array is a group of variables of the same data type and referred to by a common name. An array is contiguous block of memory locations referred by a common name.

i.e. To store 500 integer values in the variable multipleInt , you type this.

int[] multipleInt = new int[500]; //You just created a variable multipleInt[].  
//But right now it only contains 500 0s.

Types of Arrays

One-dimensional arrays

One-dimensional array is a list of variables of the same data type.

Syntax to declare a one dimensional array

//To create an one-dimensional array, you type this
type arrayName [] = new type[length];// type is like int, char, double, etc.
// ; length is how many of that type you will store

You can also declare and initialize arrays in the same statement.

For e.g.

String designations[] = {"General Manager", "Managing Director"};

Things you can do with arrays

You can print out all the values in the array. For e.g.

   int[] anArray = new int[10];  // creates a new integer array with a length of 10
		for(int fillUp= 0; fillUp<anArray.length-1;fillUp++) // This will fill the array 
                                                                     //with numbers
 		         anArray[fillUp] = (int)(Math.random()*20 +1);// fills each spot in the 
                                    //array with random numbers from 1 to 20
		for(int fillUp= 0; fillUp<anArray.length-1;fillUp++)// a '''for loop'''
			 System.out.println(anArray[fillUp]);// prints out the array

A possible output of the above will be:

20

2
4
13
6
18
12
14
10

Notice this part of the code

for(int fillUp= 0; fillUp<anArray.length-1;fillUp++)

Notice that in this part of that code:

 fillUp<anArray.length-1

, the variable fillUp must be one less the length of the array. Why do we have to do this? You may ask. Remember, the index 0 is the first value in an array/String. So if the length was 11, and the program searched for the 12th value, it would not find it, and there would be an error that says something like this: Index Out of Range .

Two-dimensional arrays

To declare two-dimensional arrays, you need to specify multiple square brackets after the array name.

Syntax to declare a two dimensional array

type array_name = new type[rows][cols];

Advantages

/* 1. You can refer to a large number of elements by just specifying the 
index number and the name of the array.
 2. These make it easy to do calculations in a loop.*/

Other Types of Arrays

You can also declare arrays like

int[][][] arrayexample = new int[2][2][2]; 
int[][][][] example2 = new int[2][2][2][2];

but it will make programming with these arrays very complicated.

The 1 dimensional array and the 2 dimensional arrays are the most commonly used

Project: Introduction to Programming in Java

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