Java Array

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

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 set of elements in a java array.

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

Types of array,

Single dimensional array
Multi  dimensional array

Single dimensional array

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

Instantiation of an Array,

arrayVariable =new datatype[size]; 

Sample

  int a[]=new int[3];//declaration and instantiation  

 a[0]=10;//initialization  
 a[1]=20;  
 a[2]=70;    

//printing array  
for(int i=0;i<a.length;i++) { //length is the property of array  
  System.out.println(a[i]);  
}
Output : 10,20,30

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]);  
}

Multi dimensional array

Syntax,

dataType[][] referenceVariable; (or) 
dataType [][]referenceVariable; (or) 
dataType referenceVariable[][]; (or) 
dataType []referenceVariable[];  

Instantiation

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

Initialize,

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;

//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

Advantages 

• An array know the type it holds, i.e., compile-time type checking. 
•  An array know its size, i.e., ask for the length. 
•  An array can hold primitive types directly.

Disadvantages 

• An array can only hold one type of objects (including primitives). 
•  Arrays are fixed size. 

Helper class,
java.util.Arrays

• Search and sort: binarySearch(), sort() 
• Comparison: equals() (many overloaded) 
• Instantiation: fill() (many overloaded) 
• Conversion: asList()