Array Programs in Java

We will study and understand Java array topics in this program. A grouping of similar types of data is called an array.

For instance, we can create an array of the string type that can hold 100 names if we need to store the names of 100 different people.

array of Strings = new String[100];
In this case, the above array is limited to 100 names. In a Java array, the number of values is always fixed.

How to Declare an Array in Java?

In Java, here is how we can declare an array.

dataType[] arrayName;

dataType – it can be primitive data types like int, char, double, byte, etc. or Java objects
arrayName – it is an identifier

For example,

double[] data;

Here, data is an array that can hold values of type double.

But, how many elements can array this hold?

A good question! In Java, we must allot memory for the array in order to define the maximum number of elements it can contain. For example,

// declare an array
double[] data;

// allocate memory
data = new double[10];

Here, the array can store 10 elements. We can also say that the size or length of the array is 10.

In Java, we can declare and allocate the memory of an array in one single statement. For example,

double[] data = new double[10];

How to Initialize Arrays in Java?

In Java, we can initialize arrays during declaration. For example,

//declare and initialize and array
int[] age = {12, 4, 5, 2, 5};

In this case, we’ve made an array named age and initialised it with the values shown in the curly brackets.

Keep in mind that we have not specified the array’s size. Here, the array’s size is automatically determined by the Java compiler by counting the number of elements in the array (i.e. 5).

Each memory region in the Java array has a corresponding number. The value is referred to as an array index. Using the index number, we may initialize arrays in Java as well.
For example,

// declare an array
int[] age = new int[5];

// initialize array
age[0] = 12;
age[1] = 4;
age[2] = 5;
..

Elements are stored in the array

Java Arrays initialization

Array indices always start from 0. That is, the first element of an array is at index 0.
If the size of an array is n, then the last element of the array will be at index n-1.

How to Access Elements of an Array in Java?

We can access the element of an array using the index number. Here is the syntax for accessing elements of an array,

// access array elements
array[index]
Let’s see an example of accessing array elements using index numbers.

Example: Access Array Elements

class Main {
 public static void main(String[] args) {
  
   int[] age = {2, 4, 6, 8, 10};

   System.out.println("Accessing Elements of Array:");
   System.out.println("First Element: " + age[0]);
   System.out.println("Second Element: " + age[1]);
   System.out.println("Third Element: " + age[2]);
   System.out.println("Fourth Element: " + age[3]);
   System.out.println("Fifth Element: " + age[4]);
 }
}
Output
Accessing Elements of Array:
First Element: 2
Second Element: 4
Third Element: 6
Fourth Element: 8
Fifth Element: 10

In the above example, notice that we are using the index number to access each element of the array.

We can use loops to access all the elements of the array at once.

Looping Through Array Elements

In Java, we can also loop through each element of the array. For example,

Example: Using For Loop

class Main {
 public static void main(String[] args) {   
   int[] age = {1, 3, 5, 7};
   System.out.println("Using for Loop:");
   for(int i = 0; i < age.length; i++) {
     System.out.println(age[i]);
   }
 }
}
Output
Using for Loop:
1
3
5
7

In the above example, we are using the for Loop in Java to iterate through each element of the array. Notice the expression inside the loop,
age.length
Here, we are using the length property of the array to get the size of the array.

We can also use the for-each loop to iterate through the elements of an array. For example,

Example: Using the for-each Loop

class Main {
 public static void main(String[] args) {  
   int[] age = {12, 8, 4, 2};
   System.out.println("Using for-each Loop:");
   for(int a : age) {
     System.out.println(a);
   }
 }
}
Output
Using for-each Loop:
12
8
4
2

Example: Compute Sum and Average of Array Elements

class Main {
 public static void main(String[] args) {
   int[] numbers = {2, -9, 0, 5, 12, -25, 22, 9, 8, 12};
   int sum = 0;
   Double average;
   for (int number: numbers) {
     sum += number;
   }  
   int arrayLength = numbers.length;
   average =  ((double)sum / (double)arrayLength);
   System.out.println("Sum = " + sum);
   System.out.println("Average = " + average);
 }
}
Output
Sum = 36
Average = 3.6

In the above example, we have created an array of named numbers. We have used the for…each loop to access each element of the array.

Inside the loop, we are calculating the sum of each element. Notice the line,

int arrayLength = number.length;

Here, we are using the length attribute of the array to calculate the size of the array. We then calculate the average using:

average = ((double)sum / (double)arrayLength);

As you can see, we are converting the int value into double. This is called type casting in Java. To learn more about typecasting, visit Java Type Casting.

Multidimensional Arrays

Arrays we have mentioned till now are called one-dimensional arrays. However, we can declare multidimensional arrays in Java.

A multidimensional array is an array of arrays. That is, each element of a multidimensional array is an array itself. For example,

double[][] matrix = {{1.2, 4.3, 4.0}, {4.1, -1.1}};

Here, we have created a multidimensional array named matrix. It is a 2-dimensional array.

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