Arrays in JAVA

What is Array

• Array is collection of similar primitive data types, object reference or collection of other array.
• All java array are treated as objects.
• We can construct java array using new keyword.
• All java array elements are initialized by their data type ‘s default value.

How to create Array in JAVA

Three Steps

1.  Array Declaration

2. Array Construction

3. Array Initialization

Array Declaration

For declaration array we use empty square brackets with the prefix and postfix of array name.

• Ex.: Declaration for primitive data types

1. Int a[];

2. Int []a;

3. Int[] a;

• Declaration for object reference

     Employee emp[];

• Array of array

     Int x[][];

Note : 2d array is always array of arrays

Construction of Array:

We can construct array by allocate memory using new keyword at run time

 

Int a[]  ;  //Array Declaration

A=new int[5];  // Array construct and able to store 5 int

Note : 

Array capacity value can be defined as non zero integer value.

Initilization of Array:

When we construct array . Then all elements of array are initilized by their array data type default value.

For Example :

Data Type	Default Value
Byte	0
Short	0
Int	0
Long	0
Float	0.0f
Double	0.0d
Boolean	False
Char	‘\u0000’
Object	null

Array Example 1.

 

public class ArrayExample {

public static void main (String[] args)
{
//Array Declaration
int[] a;
//Array COnstruction
a=new int[5];

//Loop to Read Array
for(int i=0;i<a.length;i++)
{
System.out.println(a[i]);
}

}   
}

 output

 Initilize array Elements

 

public class ArrayExample {

public static void main (String[] args)
{
//Array Declaration
int[] a;
//Array COnstruction
a=new int[5];

a[0]=10;

a[1]=20;
a[2]=30;
a[3]=40;
a[4]=50;

//Loop to Read Array
for(int i=0;i<a.length;i++)
{
System.out.println(a[i]);
} .
}

 Output

 Another Way to create array

Int[] a={12,34,45,56};

2. 2d Arrays in JAVA

• 2D Arrays is array of array.
• In 2D Arrays first we define memory for row then column.Assigning row and column memory is internal process of java.
• It is similar to2d dynamic array in C/C++;

Rectangular 2d Array

 

Declaration of 2d array

Int a[][]=new int[3][];

// First and second square brackets defined row and column respectively.

Simple memory initialization for each row

A[0]=new int[2];

A[1]=new int[2];

A[2]=new int[2];

Aa[0][0]	a[a[0][1]
Aa[1][0]	Aa[1][1]
Aa[2][0]	Aa[2][1]

3. Irregular array in Java

Int a[][]=new int[3][];

Simple memory initialization for each row

A[0]=new int[4];

A[1]=new int[2];

A[2]=new int[3];

Note : Now of rows are different.

Example 1.

import java.util.*;
public class ArrayExample {

	public static void main (String[] args)
	{
	int a[][]=new int[3][];
	 a[0]=new int[3];
	 a[1]=new int[3];
	 a[2]=new int[3];
	 
	 for(int i=0;i<a.length;i++)
	 {
		for(int j=0;j<a[i].length;j++)
		{
			Random rn=new Random();
			a[i][j]=rn.nextInt(10);
		}
	 }
	 for(int i=0;i<a.length;i++)
	 {
		for(int j=0;j<a[i].length;j++)
		{
			System.out.println("Arrays Element are "+a[i][j]);
		}
	 }
	}
}

 Output 

3. 3d array in Java

Declaration of 3d array in Java

                 Int a[][][]=new int[2][4][3];

• First Square brackets defined number of 2d arrays(here 2)
• Second square bracket defined number of rows in each 2d array.
• Third square bracket defined columns in each rows.
• a.length= no of 2d arrays
• a[i].length=no of rows in the ith 2d array
• A[i][j].length=No of elements in jth row of ith 2d array.

 

import java.util.*;
public class ArrayExample {

	public static void main (String[] args)
	{
	
		
		//3d Arrays Example 
		
		int a[][][]=new int[2][4][3];
		for(int i=0;i<a.length;i++)
		{
			for(int j=0;j<a[i].length;j++)
			{
				for(int k=0;k<a[i][j].length;k++)
				{
					a[i][j][k]=(int)(Math.random()*100);
				}
			}
		}
		for(int i=0;i<a.length;i++)
		{
			for(int j=0;j<a[i].length;j++)
			{
				for(int k=0;k<a[i][j].length;k++)
				{
					System.out.println(a[i][j][k]);
					
				}
			}
		}
	}
}

 Output

 

 

 

 Youtube Video 1(Array Introduction)

 

 Youtube Video 2(2d and 3d Array )