Arrays

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
  1. dataType[] arr; (or)  
  2. dataType []arr; (or)  
  3. dataType arr[];  
Instantiation of an Array in Java
  1. 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.
  1. //Java Program to illustrate how to declare, instantiate, initialize  
  2. //and traverse the Java array.  
  3. class Testarray{  
  4. public static void main(String args[]){  
  5. int a[]=new int[5];//declaration and instantiation  
  6. a[0]=10;//initialization  
  7. a[1]=20;  
  8. a[2]=70;  
  9. a[3]=40;  
  10. a[4]=50;  
  11. //traversing array  
  12. for(int i=0;i<a.length;i++)//length is the property of array  
  13. System.out.println(a[i]);  
  14. }} 
Output:
10
20
70
40
50

Declaration, Instantiation and Initialization of Java Array

We can declare, instantiate and initialize the java array together by:
  1. int a[]={33,3,4,5};//declaration, instantiation and initialization  
Let's see the simple example to print this array.
  1. //Java Program to illustrate the use of declaration, instantiation   
  2. //and initialization of Java array in a single line  
  3. class Testarray1{  
  4. public static void main(String args[]){  
  5. int a[]={33,3,4,5};//declaration, instantiation and initialization  
  6. //printing array  
  7. for(int i=0;i<a.length;i++)//length is the property of array  
  8. System.out.println(a[i]);  
  9. }}  
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.
  1. //Java Program to demonstrate the way of passing an array  
  2. //to method.  
  3. class Testarray2{  
  4. //creating a method which receives an array as a parameter  
  5. static void min(int arr[]){  
  6. int min=arr[0];  
  7. for(int i=1;i<arr.length;i++)  
  8.  if(min>arr[i])  
  9.   min=arr[i];  
  10.   
  11. System.out.println(min);  
  12. }  
  13.   
  14. public static void main(String args[]){  
  15. int a[]={33,3,4,5};//declaring and initializing an array  
  16. min(a);//passing array to method  
  17. }}  
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.
  1. //Java Program to demonstrate the way of passing an anonymous array  
  2. //to method.  
  3. public class TestAnonymousArray{  
  4. //creating a method which receives an array as a parameter  
  5. static void printArray(int arr[]){  
  6. for(int i=0;i<arr.length;i++)  
  7. System.out.println(arr[i]);  
  8. }  
  9.   
  10. public static void main(String args[]){  
  11. printArray(new int[]{10,22,44,66});//passing anonymous array to method  
  12. }}  
Output:
10
22
44
66

Returning Array from the Method

We can also return an array from the method in Java.
  1. //Java Program to return an array from the method  
  2. class TestReturnArray{  
  3. //creating method which returns an array  
  4. static int[] get(){  
  5. return new int[]{10,30,50,90,60};  
  6. }  
  7.   
  8. public static void main(String args[]){  
  9. //calling method which returns an array  
  10. int arr[]=get();  
  11. //printing the values of an array  
  12. for(int i=0;i<arr.length;i++)  
  13. System.out.println(arr[i]);  
  14. }}  
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.
  1. //Java Program to demonstrate the case of   
  2. //ArrayIndexOutOfBoundsException in a Java Array.  
  3. public class TestArrayException{  
  4. public static void main(String args[]){  
  5. int arr[]={50,60,70,80};  
  6. for(int i=0;i<=arr.length;i++){  
  7. System.out.println(arr[i]);  
  8. }  
  9. }}  
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
  1. dataType[][] arrayRefVar; (or)  
  2. dataType [][]arrayRefVar; (or)  
  3. dataType arrayRefVar[][]; (or)  
  4. dataType []arrayRefVar[];   
Example to instantiate Multidimensional Array in Java
  1. int[][] arr=new int[3][3];//3 row and 3 column  
Example to initialize Multidimensional Array in Java
  1. arr[0][0]=1;  
  2. arr[0][1]=2;  
  3. arr[0][2]=3;  
  4. arr[1][0]=4;  
  5. arr[1][1]=5;  
  6. arr[1][2]=6;  
  7. arr[2][0]=7;  
  8. arr[2][1]=8;  
  9. arr[2][2]=9;  

Example of Multidimensional Java Array

Let's see the simple example to declare, instantiate, initialize and print the 2Dimensional array.
  1. //Java Program to illustrate the use of multidimensional array  
  2. class Testarray3{  
  3. public static void main(String args[]){  
  4. //declaring and initializing 2D array  
  5. int arr[][]={{1,2,3},{2,4,5},{4,4,5}};  
  6. //printing 2D array  
  7. for(int i=0;i<3;i++){  
  8.  for(int j=0;j<3;j++){  
  9.    System.out.print(arr[i][j]+" ");  
  10.  }  
  11.  System.out.println();  
  12. }  
  13. }}  
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.
  1. //Java Program to illustrate the jagged array  
  2. class TestJaggedArray{  
  3.     public static void main(String[] args){  
  4.         //declaring a 2D array with odd columns  
  5.         int arr[][] = new int[3][];  
  6.         arr[0] = new int[3];  
  7.         arr[1] = new int[4];  
  8.         arr[2] = new int[2];  
  9.         //initializing a jagged array  
  10.         int count = 0;  
  11.         for (int i=0; i<arr.length; i++)  
  12.             for(int j=0; j<arr[i].length; j++)  
  13.                 arr[i][j] = count++;  
  14.    
  15.         //printing the data of a jagged array   
  16.         for (int i=0; i<arr.length; i++){  
  17.             for (int j=0; j<arr[i].length; j++){  
  18.                 System.out.print(arr[i][j]+" ");  
  19.             }  
  20.             System.out.println();//new line  
  21.         }  
  22.     }  
  23. }  
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.
  1. //Java Program to get the class name of array in Java  
  2. class Testarray4{  
  3. public static void main(String args[]){  
  4. //declaration and initialization of array  
  5. int arr[]={4,4,5};  
  6. //getting the class name of Java array  
  7. Class c=arr.getClass();  
  8. String name=c.getName();  
  9. //printing the class name of Java array   
  10. System.out.println(name);  
  11.   
  12. }}  
Output:
I

Copying a Java Array

We can copy an array to another by the arraycopy() method of System class.
Syntax of arraycopy method
  1. public static void arraycopy(  
  2. Object src, int srcPos,Object dest, int destPos, int length  
  3. )  

Example of Copying an Array in Java

  1. //Java Program to copy a source array into a destination array in Java  
  2. class TestArrayCopyDemo {  
  3.     public static void main(String[] args) {  
  4.         //declaring a source array  
  5.         char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e',  
  6.                 'i', 'n', 'a', 't', 'e', 'd' };  
  7.         //declaring a destination array  
  8.         char[] copyTo = new char[7];  
  9.         //copying array using System.arraycopy() method  
  10.         System.arraycopy(copyFrom, 2, copyTo, 0, 7);  
  11.         //printing the destination array  
  12.         System.out.println(String.valueOf(copyTo));  
  13.     }  
  14. }  
Output:
caffein

Addition of 2 Matrices in Java

Let's see a simple example that adds two matrices.
  1. //Java Program to demonstrate the addition of two matrices in Java  
  2. class Testarray5{  
  3. public static void main(String args[]){  
  4. //creating two matrices  
  5. int a[][]={{1,3,4},{3,4,5}};  
  6. int b[][]={{1,3,4},{3,4,5}};  
  7.   
  8. //creating another matrix to store the sum of two matrices  
  9. int c[][]=new int[2][3];  
  10.   
  11. //adding and printing addition of 2 matrices  
  12. for(int i=0;i<2;i++){  
  13. for(int j=0;j<3;j++){  
  14. c[i][j]=a[i][j]+b[i][j];  
  15. System.out.print(c[i][j]+" ");  
  16. }  
  17. System.out.println();//new line  
  18. }  
  19.   
  20. }}  
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.


Let's see a simple example to multiply two matrices of 3 rows and 3 columns.
  1. //Java Program to multiply two matrices  
  2. public class MatrixMultiplicationExample{  
  3. public static void main(String args[]){  
  4. //creating two matrices    
  5. int a[][]={{1,1,1},{2,2,2},{3,3,3}};    
  6. int b[][]={{1,1,1},{2,2,2},{3,3,3}};    
  7.     
  8. //creating another matrix to store the multiplication of two matrices    
  9. int c[][]=new int[3][3];  //3 rows and 3 columns  
  10.     
  11. //multiplying and printing multiplication of 2 matrices    
  12. for(int i=0;i<3;i++){    
  13. for(int j=0;j<3;j++){    
  14. c[i][j]=0;      
  15. for(int k=0;k<3;k++)      
  16. {      
  17. c[i][j]+=a[i][k]*b[k][j];      
  18. }//end of k loop  
  19. System.out.print(c[i][j]+" ");  //printing matrix element  
  20. }//end of j loop  
  21. System.out.println();//new line    
  22. }    
  23. }}  
Output:
6 6 6 
12 12 12 
18 18 18
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