Array in Java

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

In java, array is an object the contains elements of similar data type. It is a data structure where we store similar elements. We can store only fixed elements in an array.

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

Advantage of Array

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

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Disadvantage of Array

• Size Limit: We can store only 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.

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Types of Array

There are two types of array.

• Single Dimensional Array
• Multidimensional Array

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Single Dimensional Array

Syntax to Declare an Array in java

1. dataType[] arrayRefVar; (or)  
2. dataType []arrayRefVar; (or)  
3. dataType arrayRefVar[];  

Instantiation of an Array in java

1. arrayRefVar=new datatype[size];  

Example of single dimensional java array

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

1. class B{  
2. public static void main(String args[]){  
3.   
4. int a[]=new int[5];//declaration and instantiation  
5. a[0]=10;//initialization  
6. a[1]=20;  
7. a[2]=70;  
8. a[3]=40;  
9. a[4]=50;  
10.   
11. //printing array  
12. for(int i=0;i<a.length;i++)//length is the property of array  
13. System.out.println(a[i]);  
14.   
15. }}  

Output: 10
       20
       70
       40
       50
      

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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. class B{  
2. public static void main(String args[]){  
3.   
4. int a[]={33,3,4,5};//declaration, instantiation and initialization  
5.   
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.   
10. }}  

Output:33
       3
       4
       5
   

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Passing Java Array in the method

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

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

1. class B{  
2. static void min(int arr[]){  
3. int min=arr[0];  
4. for(int i=1;i<arr.length;i++)  
5.  if(min>arr[i])  
6.   min=arr[i];  
7.   
8. System.out.println(min);  
9. }  
10.   
11. public static void main(String args[]){  
12.   
13. int a[]={33,3,4,5};  
14. min(a);//passing array in the method  
15.   
16. }}  

Output:3

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Multidimensional array

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. class B{  
2. public static void main(String args[]){  
3.   
4. //declaring and initializing 2D array  
5. int arr[][]={{1,2,3},{2,4,5},{4,4,5}};  
6.   
7. //printing 2D array  
8. for(int i=0;i<3;i++){  
9.  for(int j=0;j<3;j++){  
10.    System.out.print(arr[i][j]+" ");  
11.  }  
12.  System.out.println();  
13. }  
14.   
15. }}  

Output:1 2 3
       2 4 5
       4 4 5

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What is class name of java array?

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

1. class B{  
2. public static void main(String args[]){  
3.   
4. int arr[]={4,4,5};  
5.   
6. Class c=arr.getClass();  
7. String name=c.getName();  
8.   
9. System.out.println(name);  
10.   
11. }}  

Output:I

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Copying an 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 arraycopy method

1. class ArrayCopyDemo {  
2.     public static void main(String[] args) {  
3.         char[] copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e',  
4.                 'i', 'n', 'a', 't', 'e', 'd' };  
5.         char[] copyTo = new char[7];  
6.   
7.         System.arraycopy(copyFrom, 2, copyTo, 0, 7);  
8.         System.out.println(new String(copyTo));  
9.     }  
10. }  

Output:caffein

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Addition 2 matrices

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

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

Output:2 6 8
       6 8 10