Java Array

Summary: in this tutorial, you will learn how to use Java array to store multiple values of the same data type under a single variable name.

Introduction to Java array #

So far, you have learned how to declare variables that hold a single value e.g., an integer, a double, and a string.

In Java, an array is a data structure that allows you to store multiple values of the same data type under a single variable. Arrays allow you to manage collections of data efficiently.

Declaring an array #

To declare an array, you specify the data type of the elements it will hold, followed by square brackets [] and the array name:

dataType [] arrayName;Copy

For example, the following declares an array that stores integers:

int [] numbers;Copy

Initializing an array #

If you know the elements that an array will hold, you can provide the values of the elements at the time of declaration. For example, the following declares an array and initializes its elements that include 1, 2, and 3:

int[] numbers = { 1, 2, 3 };Copy

Getting the array’s length #

To determine the number of elements of an array, you use the length property. For example:

public class App {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3};
        System.out.println(numbers.length); //3
    }
}Copy

Output:

3Copy

In this example, we use the length property to get the number of elements of the numbers array.

Accessing array elements #

To access an array element, you can use its index. The first element of the array starts at 0. For example, the following shows how to access the first and second elements of the numbers array:

int[] numbers = {1, 2, 3};
int first = numbers[0];
int second = numbers[1];Copy

Modifying array elements #

To modify an array element, you assign a value to it using the assignment operator =. For example, the following changes the third element of the numbers array to 30:

public class App {
    public static void main(String[] args) {
        int[] numbers = { 1, 2, 3 };
        numbers[2] = 30;

        System.out.println(numbers[2]); // 30
    }
}Copy

Note that the third element has an index 2.

Dynamic initialization #

If you don’t know the elements of an array upfront, you can specify the size of the array:

int[] numbers = new int[3];Copy

Later, you can assign values to individual elements:

numbers[0] = 1; 
numbers[1] = 2; 
numbers[2] = 3;Copy

Iterating through arrays #

To iterate through an array, you can use a for loop and index-based access. For example, the following uses the for loop to output the elements of the numbers array to the screen:

public class App {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3};
        for (int i = 0; i < numbers.length; i++) {
            System.out.println(numbers[i]);
        }
    }
}Copy

You can also use enhanced for loop (also known as for-each loop) to simplify array iteration:

public class App {
    public static void main(String[] args) {
        int[] numbers = {1, 2, 3};

        for (int number : numbers) {
            System.out.println(number);
        }
    }
}Copy

Summary #

• Use an array to store multiple values of the same data type under a single variable.
• Use the length property to get the number of elements in an array.
• Arrays are zero-based indexing, meaning the first element always starts at zero.
• Use a for loop or for-each loop to iterate over elements of an array.