Normally, an array is a collection of similar type of elements that have a contiguous memory location.

Java array is an object which contains elements of a similar data type. It is a data structure where we store similar elements. We can store only a fixed set of elements in a Java array.

Array in java is index-based, the first element of the array is stored at the 0 index.

java array

Advantages

  • Code Optimization: It makes the code optimized, we can retrieve or sort the data efficiently.
  • Random access: We can get any data located at an index position.

Disadvantages

  • Size Limit: We can store only the fixed size of elements in the array. It doesn’t grow its size at runtime. To solve this problem, collection framework is used in Java which grows automatically.

Types of Array in java

There are two types of array.

  • Single Dimensional Array
  • Multidimensional Array

Single Dimensional Array in Java

Syntax to Declare an Array in Java

dataType[] arr; (or)  
dataType []arr; (or)  
dataType arr[];

Instantiation of an Array in Java

arrayRefVar=new datatype[size];

Example of Java Array

Let’s see the simple example of java array, where we are going to declare, instantiate, initialize and traverse an array.

//Java Program to illustrate how to declare, instantiate, initialize  
//and traverse the Java array.  
class Testarray{  
public static void main(String args[]){  
int a[]=new int[5];//declaration and instantiation  
a[0]=10;//initialization  
a[1]=20;  
a[2]=70;  
a[3]=40;  
a[4]=50;  
//traversing array  
for(int i=0;i<a.length;i++)//length is the property of array  
System.out.println(a[i]);  
}}

Output:

10
20
70
40
50

Declaration, Instantiation and Initialization of Java Array

We can declare, instantiate and initialize the java array together by:

int a[]={33,3,4,5};//declaration, instantiation and initialization

Let’s see the simple example to print this array.

//Java Program to illustrate the use of declaration, instantiation   
//and initialization of Java array in a single line  
class Testarray1{  
public static void main(String args[]){  
int a[]={33,3,4,5};//declaration, instantiation and initialization  
//printing array  
for(int i=0;i<a.length;i++)//length is the property of array  
System.out.println(a[i]);  
}}

Output:

33
3
4
5

Passing Array to Method in Java

We can pass the java array to method so that we can reuse the same logic on any array.

Let’s see the simple example to get the minimum number of an array using a method.

//Java Program to demonstrate the way of passing an array  
//to method.  
class Testarray2{  
//creating a method which receives an array as a parameter  
static void min(int arr[]){  
int min=arr[0];  
for(int i=1;i<arr.length;i++) if(min>arr[i])  
  min=arr[i];  
  
System.out.println(min);  
}  
  
public static void main(String args[]){  
int a[]={33,3,4,5};//declaring and initializing an array  
min(a);//passing array to method  
}}

Output:

3

Anonymous Array in Java

Java supports the feature of an anonymous array, so you don’t need to declare the array while passing an array to the method.

//Java Program to demonstrate the way of passing an anonymous array  
//to method.  
public class TestAnonymousArray{  
//creating a method which receives an array as a parameter  
static void printArray(int arr[]){  
for(int i=0;i<arr.length;i++)  
System.out.println(arr[i]);  
}  
  
public static void main(String args[]){  
printArray(new int[]{10,22,44,66});//passing anonymous array to method  
}}

Output:

10
22
44
66

Returning Array from the Method

We can also return an array from the method in Java.

//Java Program to return an array from the method  
class TestReturnArray{  
//creating method which returns an array  
static int[] get(){  
return new int[]{10,30,50,90,60};  
}  
  
public static void main(String args[]){  
//calling method which returns an array  
int arr[]=get();  
//printing the values of an array  
for(int i=0;i<arr.length;i++)  
System.out.println(arr[i]);  
}}

Output:

10
30
50
90
60

ArrayIndexOutOfBoundsException

The Java Virtual Machine (JVM) throws an ArrayIndexOutOfBoundsException if length of the array in negative, equal to the array size or greater than the array size while traversing the array.

//Java Program to demonstrate the case of   
//ArrayIndexOutOfBoundsException in a Java Array.  
public class TestArrayException{  
public static void main(String args[]){  
int arr[]={50,60,70,80};  
for(int i=0;i<=arr.length;i++){  
System.out.println(arr[i]);  
}  
}}

Output:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
	at TestArrayException.main(TestArrayException.java:5)
50
60
70
80

Multidimensional Array in Java

In such case, data is stored in row and column based index (also known as matrix form).

Syntax to Declare Multidimensional Array in Java

dataType[][] arrayRefVar; (or)  
dataType [][]arrayRefVar; (or)  
dataType arrayRefVar[][]; (or)  
dataType []arrayRefVar[];

Example to instantiate Multidimensional Array in Java

int[][] arr=new int[3][3];//3 row and 3 column

Example to initialize Multidimensional Array in Java

arr[0][0]=1;  
arr[0][1]=2;  
arr[0][2]=3;  
arr[1][0]=4;  
arr[1][1]=5;  
arr[1][2]=6;  
arr[2][0]=7;  
arr[2][1]=8;  
arr[2][2]=9;

Example of Multidimensional Java Array

Let’s see the simple example to declare, instantiate, initialize and print the 2Dimensional array.

//Java Program to illustrate the use of multidimensional array  
class Testarray3{  
public static void main(String args[]){  
//declaring and initializing 2D array  
int arr[][]={{1,2,3},{2,4,5},{4,4,5}};  
//printing 2D array  
for(int i=0;i<3;i++){  
 for(int j=0;j<3;j++){  
   System.out.print(arr[i][j]+" ");  
 }  
 System.out.println();  
}  
}}

Output:

1 2 3
2 4 5
4 4 5

Jagged Array in Java

If we are creating odd number of columns in a 2D array, it is known as a jagged array. In other words, it is an array of arrays with different number of columns.

//Java Program to illustrate the jagged array  
class TestJaggedArray{  
    public static void main(String[] args){  
        //declaring a 2D array with odd columns  
        int arr[][] = new int[3][];  
        arr[0] = new int[3];  
        arr[1] = new int[4];  
        arr[2] = new int[2];  
        //initializing a jagged array  
        int count = 0;  
        for (int i=0; i<arr.length; i++)  
            for(int j=0; j<arr[i].length; j++)  
                arr[i][j] = count++;  
   
        //printing the data of a jagged array   
        for (int i=0; i<arr.length; i++){  
            for (int j=0; j<arr[i].length; j++){  
                System.out.print(arr[i][j]+" ");  
            }  
            System.out.println();//new line  
        }  
    }  
}

Output:

0 1 2 
3 4 5 6 
7 8

What is the class name of Java array?

In Java, an array is an object. For array object, a proxy class is created whose name can be obtained by getClass().getName() method on the object.

//Java Program to get the class name of array in Java  
class Testarray4{  
public static void main(String args[]){  
//declaration and initialization of array  
int arr[]={4,4,5};  
//getting the class name of Java array  
Class c=arr.getClass();  
String name=c.getName();  
//printing the class name of Java array   
System.out.println(name);  
  
}}

Output:

I

Copying a Java Array

We can copy an array to another by the arraycopy() method of System class.

Syntax of arraycopy method

public static void arraycopy(  
Object src, int srcPos,Object dest, int destPos, int length  
)

Example of Copying an Array in Java

//Java Program to copy a source array into a destination array in Java  
class TestArrayCopyDemo {  
    public static void main(String[] args) {  
        //declaring a source array  
        char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e',  
                'i', 'n', 'a', 't', 'e', 'd' };  
        //declaring a destination array  
        char[] copyTo = new char[7];  
        //copying array using System.arraycopy() method  
        System.arraycopy(copyFrom, 2, copyTo, 0, 7);  
        //printing the destination array  
        System.out.println(String.valueOf(copyTo));  
    }  
}

Output:

caffein

Addition of 2 Matrices in Java

Let’s see a simple example that adds two matrices.

//Java Program to demonstrate the addition of two matrices in Java  
class Testarray5{  
public static void main(String args[]){  
//creating two matrices  
int a[][]={{1,3,4},{3,4,5}};  
int b[][]={{1,3,4},{3,4,5}};  
  
//creating another matrix to store the sum of two matrices  
int c[][]=new int[2][3];  
  
//adding and printing addition of 2 matrices  
for(int i=0;i<2;i++){  
for(int j=0;j<3;j++){  
c[i][j]=a[i][j]+b[i][j];  
System.out.print(c[i][j]+" ");  
}  
System.out.println();//new line  
}  
  
}}

Output:

2 6 8
6 8 10

Multiplication of 2 Matrices in Java

In the case of matrix multiplication, a one-row element of the first matrix is multiplied by all the columns of the second matrix which can be understood by the image given below.

Matrix Multiplication in Java

Let’s see a simple example to multiply two matrices of 3 rows and 3 columns.

//Java Program to multiply two matrices  
public class MatrixMultiplicationExample{  
public static void main(String args[]){  
//creating two matrices    
int a[][]={{1,1,1},{2,2,2},{3,3,3}};    
int b[][]={{1,1,1},{2,2,2},{3,3,3}};    
    
//creating another matrix to store the multiplication of two matrices    
int c[][]=new int[3][3];  //3 rows and 3 columns  
    
//multiplying and printing multiplication of 2 matrices    
for(int i=0;i<3;i++){    
for(int j=0;j<3;j++){    
c[i][j]=0;      
for(int k=0;k<3;k++)      
{      
c[i][j]+=a[i][k]*b[k][j];      
}//end of k loop  
System.out.print(c[i][j]+" ");  //printing matrix element  
}//end of j loop  
System.out.println();//new line    
}    
}}

Output:

6 6 6 
12 12 12 
18 18 18