Java – Arrays

Multiple values can be stored in a single variable using arrays. In Java, an array’s items must all be of the same datatype.

Create an Array

It begins by declaring the array’s datatype, which is encased in square brackets [], and then the array’s name.

Initialize an Array

A comma can be used to separate the items of Java Arrays, and curly brackets can be used to enclose them. Please keep in mind that declaring an array does not allocate memory for it. An array must be initialised before it may be allocated memory. If the array was not initialised when it was declared, it must be initialised with the new keyword, followed by the data type and array size wrapped in square brackets []. For numerous declaration and initialization procedures, check the syntax below.

Syntax

//both declaration methods are valid in Java
int[] MyArray;
int MyArray[];

//declaration and initialization of  
//an integer array separately
int[] MyArray;
MyArray = new int[5]; //size of array is 5 
MyArray[0] = 10;      //first element is 10.

//declaration and initialization of an string 
//array in a single line
String[] MyArray = {"MON", "TUE", "WED"};

//Another method of declaration and initialization  
//of an string array in a single line
String[] MyArray = new String[5];

Access element of an Array

The index number of an array element can be used to access it. In Java, an array’s index number begins with 0 as illustrated in the diagram below:

The following example shows how to use an array’s index number to retrieve its elements.

public class MyClass {
  public static void main(String[] args) {
    //creating an array with 5 elements
    String[] weekday = {"MON", "TUE", "WED", "THU", "FRI"}; 
    
    //accessing the element with index number 4
    System.out.println(weekday[4]); 
  }
}

FRI

Modify elements of an Array

Any element of an Array can be changed by assigning a new value to its index number.

public class MyClass {
  public static void main(String[] args) {
    String[] weekday = {"MON", "TUE", "WED", "THU", "FRI"}; 
    weekday[0] = "MON_new";
    weekday[3] = "THU_new";
    System.out.println(weekday[0]); 
    System.out.println(weekday[3]); 
  }
}

MON_new
THU_new

Number of elements in Array

The length property of an array may be used to estimate the number of elements in the array.

public class MyClass {
  public static void main(String[] args) {
    String[] weekday = {"MON", "TUE", "WED", "THU", "FRI"}; 
    System.out.println(weekday.length); 
  }
}

5

Loop over an Array

We may access each element of an Array using a for loop or a while loop. We may also use the for-each loop, which is only available for looping through the items of an array.

For Loop over an Array

The for loop is used in the example below to access all items of the provided array.

public class MyClass {
  public static void main(String[] args) {
    String[] weekday = {"MON", "TUE", "WED", "THU", "FRI"};

    for(int i = 0; i < weekday.length; i++) { 
      System.out.println(weekday[i]);   	
    }  
  }
}

The output of the above code will be:

MON
TUE
WED
THU
FRI

While Loop over an Array

Similarly, the while loop may be used to access array items.

public class MyClass {
  public static void main(String[] args) {
    int[] numbers = {10, 20, 30, 40, 50};
    int i = 0;
    while(i < numbers.length) { 
      System.out.println(numbers[i]);   
      i++;	
    }  
  }
}

10
20
30
40
50

For-each over an Array

Syntax

for(datatype i : MyArray){
  statements;
}

public class MyClass {
  public static void main(String[] args) {
    int[] numbers = {10, 20, 30, 40, 50};
    for ( int i : numbers) { 
      System.out.println(i);   	
    }  
  }
}

The output of the above code will be:

10
20
30
40
50

Multi-dimensional Array

Arrays of arrays can be considered multi-dimensional arrays. You can define arrays of any size in Java. To access items of a multi-dimensional array, use a For-loop or While-loop.

Syntax

//2-dimension array
int[][] MyArray;    

//3-dimension array
int[][][] MyArray; 

//2-dimensional array
int[][] MyArray = {{10,20,30},{100,200}}; 

public class MyClass {
  public static void main(String[] args) {
    int[][] numbers = {{10, 20, 30}, {40, 50, 60}};
    for(int i = 0; i < 2; i++) {
      for(int j = 0; j < 3; j++) {
        System.out.println(numbers[i][j]);
      }
    }     
  }
}

The output of the above code will be:

10
20 
30 
40 
50 
60

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