Arrays in Java

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An Array is a dynamically created object where we store similar elements. By declaring an array, memory space is allocate for values of a particular type. At the time of creation, the length of the array must be specified and remains constant

A Java array variable can also be declared like other variables with [] after the data type.

The variables in the array are ordered and each have an index beginning from 0.

 12

56

66

15

89

47

33

69

Index ->0      1             2          3             4               5               6          7

  Array Length = 8

  First Index=0

  Last Index = 7

How to declare an Array??

ArrayDataType[] ArrayName;
String[] days;

ArrayDataType – can be Int, Float

ArrayName – name assigned to array

 Creating Array

 You can create array by using new operator.

arrayRefVar = new dataType[arraySize];

Declaring an array variable, creating an array, and assigning the reference of the array to the variable can be combine in one statement, as shown below:

   dataType[] arrayRefVar = new dataType[arraySize];

Alternatively, you can create arrays as follows:

dataType[] arrayRefVar = {value0, value1, …, valuek}; 

 The array elements are access through the index.

 Array indices are 0-based; that is, they start from 0 to arrayRefVar.length-1.

Assigning values to an Array

How to initialize an array during declaration.

    ArrayType [] ArrayName = New ArrayType [Size of an Array];
String[] Days = new String[6];
Days[0] = “Monday”;
Days[1]=”Tuesday”;
Days[2]=”Wednesday”;
Days[3]=”Thursday”;
Days[4]=”Friday”;
Days[5]=”Saturday”;
Days[6]=”Sunday”;

    Another way

    String[] Days =  {“Monday”,”Tuesday”,”Wednesday”,”Thursday”,”Friday”,”Saturday”,”Sunday”}

Mon

Day[0]   
Tues

Day[1]
Wed

Day[2]
Thurs

Day[3]
Fri

Day[4]
Sat

Day[5]
Sun

Day[6]
public class Array_Example {
          public static void main(String[] args) {             
                   String[] Days= {"Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"};
                   
                   //Length of Array
                   int len=Days.length;
                   //Access first element
                   System.out.println("First element in Array: "+Days[0]);
                    //Last element
                   System.out.println("First element in Array: "+Days[len-1]);
                     //Print values
                   for(int i=0;i<len-1;i++)
                   {
                       System.out.println("Value stored at position "+i+" is "+Days[i]);
                   }
          }
   }

   Output
   First element in Array: Monday
   First element in Array: Sunday
   Value stored at position 0 is Monday
   Value stored at position 1 is Tuesday
   Value stored at position 2 is Wednesday
   Value stored at position 3 is Thursday
   Value stored at position 4 is Friday
   Value stored at position 5 is Saturday

Passing an Array to a Method

Array can be passed easily to a method as parameters, just as if we pass integers and strings to methods. 

public class Array_Example {
          public static void main(String[] args) {      
                   String[] Days= {"Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"};
                   
                   //Pass array as method
                    print_arrays(Days);
          }
          public static void print_arrays(String[]array)
          {
                   int len=array.length;
                   //Print values
                   for(int i=0;i<len-1;i++)
                   {
                             System.out.println("Value stored at position "+i+" is "+array[i]);
                   }
          }
   }

    Output
    Value stored at position 0 is Monday
    Value stored at position 1 is Tuesday
    Value stored at position 2 is Wednesday
    Value stored at position 3 is Thursday
    Value stored at position 4 is Friday
    Value stored at position 5 is Saturday

    Multi Dimensional Arrays

    It is also possible to create an array of arrays known as multidimensional array. For example,

    int[][] a = new int[3][4];

    int[][] a = {  {1, 2, 3},{4, 5, 6, 9},{7}};  

 Column1Column 2Column 3Column 4
Row 11         a[0][0]2     a[0][1]3        a[0][2]  a[0][3]
Row 24                a[1][0]5     a[1][1]6      a[1][2]9     a[1][3]
Row 37                a[2][0] a[2][1]  a[2][2] a[2][3]
public class Multidimensional_Array {
          public static void main(String[] args) {
                   int a[][] = {{1,2,3},
                                      {4,5,6,9},
                                      {7}};    
                   //print length of columns
                   System.out.println("Length of Row 1 is :"+a[0].length);
                   System.out.println("Length of Row 2 is :"+a[1].length);
                   System.out.println("Length of Row 3 is :"+a[2].length);  
                   System.out.println("----------------------");
                   //Print all elements of array
                   for (int i=0;i<a.length;i++)
                   {
                             for (int j=0;j<a[i].length;j++)
                             {
                                      System.out.println(a[i][j]);
                             }
                       }  
                   }
          }

    Output
    Length of Row 1 is :3
    Length of Row 2 is :4
    Length of Row 3 is :1
----------------------
    1
    2
    3
    4
    5
    6
    9
    7

What is the difference between array and string?

  • Arrays can have any data type of any length while strings are usually ASCII characters that are terminated with a null character ‘\0’
  • An array of characters is mutable, in other words, you can replace a character in an array of characters by overwriting the memory location for that character.
  • A String is not mutable, in other words, to “replace” a character in a String, you must build a new String with the desired character in place (copying the non-changing parts from the old String).                                        
  • All string literals are stored in the String constant pool. They remain in the pool until they became eligible for the garbage collection, while a Character array is stored in heap memory.                                               
  • Character array is preferred over string for storing passwords in java. As string is immutable, it makes string vulnerable for storing passwords, as we cannot get rid of passwords after use until garbage collector collects it.

2 thoughts on “Arrays in Java

  1. Function is the concept of C language. In Java, it is called methods. To know more about methods, please go through below linkhttps://configureselenium.blogspot.com/2019/04/methods-in-java.html

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