Convert Char Array to Int Array in Java

Last updated: January 8, 2024

Written by: Abderrahim Azhrioun

Reviewed by: Luis Javier Peris

Java Array

Refactor Java code safely — and automatically — with OpenRewrite.

Refactoring big codebases by hand is slow, risky, and easy to put off. That’s where OpenRewrite comes in. The open-source framework for large-scale, automated code transformations helps teams modernize safely and consistently.

Each month, the creators and maintainers of OpenRewrite at Moderne run live, hands-on training sessions — one for newcomers and one for experienced users. You’ll see how recipes work, how to apply them across projects, and how to modernize code with confidence.

Join the next session, bring your questions, and learn how to automate the kind of work that usually eats your sprint time.

Distributed systems often come with complex challenges such as service-to-service communication, state management, asynchronous messaging, security, and more.

Dapr (Distributed Application Runtime) provides a set of APIs and building blocks to address these challenges, abstracting away infrastructure so we can focus on business logic.

In this tutorial, we'll focus on Dapr's pub/sub API for message brokering. Using its Spring Boot integration, we'll simplify the creation of a loosely coupled, portable, and easily testable pub/sub messaging system:

>> Flexible Pub/Sub Messaging With Spring Boot and Dapr

1. Overview

In this short tutorial, we’ll explore different ways of converting a char array to an int array in Java.

First, we’ll use methods and classes from Java 7. Then, we’ll see how to achieve the same objective using Java 8 Stream API.

2. Using Character Class

The Character class wraps a char value in an object. It provides various methods to work and manipulate primitive characters as objects.

Among these handy methods, we find getNumericValue() and digit(). So, let’s dig in and see how to use them to convert a char array into an int array.

2.1. Character#getNumericValue()

This method offers a straightforward and concise way to return the int value of the given character. For instance, the character ‘6’ will return 6.

So, let’s see in action:

int[] usingGetNumericValueMethod(char[] chars) {
    if (chars == null) {
        return null;
    }

    int[] ints = new int[chars.length];
    for (int i = 0; i < chars.length; i++) {
        ints[i] = Character.getNumericValue(chars[i]);
    }

    return ints;
}

As we can see, we iterated through the char array. Then, we called the getNumericValue() to get the integer value of each character.

An important caveat is that if the specified character does not have any int value, -1 is returned instead.

Please bear in mind that we can rewrite our traditional loop in a more functional way:

Arrays.setAll(ints, i -> Character.getNumericValue(chars[i]));

Now, let’s add a test case:

@Test
void givenCharArray_whenUsingGetNumericValueMethod_shouldGetIntArray() {
    int[] expected = { 2, 3, 4, 5 };
    char[] chars = { '2', '3', '4', '5' };
    int[] result = CharArrayToIntArrayUtils.usingGetNumericValueMethod(chars);

    assertArrayEquals(expected, result);
}

2.2. Character#digit()

Typically, digit(char ch, int radix) is another method that we can use to address our central question. This method returns the numeric value of the given character based on the specified radix.

Now, let’s exemplify how to use digit() to convert an array of characters into an array of integers:

int[] usingDigitMethod(char[] chars) {
    int[] ints = new int[chars.length];
    for (int i = 0; i < chars.length; i++) {
        ints[i] = Character.digit(chars[i], 10);
    }

    return ints;
}

In short, the most common radix is 10, which denotes the decimal system (0-9). For example, the character ‘7’ in base 10 is simply equal to 7.

Lastly, we’ll create another test case to confirm our method:

@Test
void givenCharArray_whenUsingDigitMethod_shouldGetIntArray() {
    int[] expected = { 1, 2, 3, 6 };
    char[] chars = { '1', '2', '3', '6' };
    int[] result = CharArrayToIntArrayUtils.usingDigitMethod(chars);

    assertArrayEquals(expected, result);
}

3. Using the Stream API

Alternatively, we can use the stream API to process the char array to int array conversion. So, let’s see it in practice:

int[] usingStreamApiMethod(char[] chars) {

    return new String(chars).chars()
      .map(c -> c - 48)
      .toArray();
}

As shown above, we created a String object from the char array. Then, we used the chars() and map() methods to transform each character into an int value.

Please note that the character ‘0’ is 48 in ASCII, ‘1’ is 49, and so on. Thus, ‘0’ – 48 equals 0, and so on. This why subtracting by 48 translates the characters ‘0’..’9′ to the values 0..9.

Next, let’s add another test case:

@Test
void givenCharArray_whenUsingStreamApi_shouldGetIntArray() {
    int[] expected = { 9, 8, 7, 6 };
    char[] chars = { '9', '8', '7', '6' };
    int[] result = CharArrayToIntArrayUtils.usingStreamApiMethod(chars);

    assertArrayEquals(expected, result);
}

4. Using Integer#parseInt()

parseInt() is another great option to consider when converting a char into an int. This method lets us get the primitive int value of a given string:

int[] usingParseIntMethod(char[] chars) {

    int[] ints = new int[chars.length];
    for (int i = 0; i < chars.length; i++) {
        ints[i] = Integer.parseInt(String.valueOf(chars[i]));
    }

    return ints;
}

Here, we need to convert each character into a string first before returning the int value.

As always, we’ll create a test case to unit test our method:

@Test
void givenCharArray_whenUsingParseIntMethod_shouldGetIntArray() {
    int[] expected = { 9, 8, 7, 6 };
    char[] chars = { '9', '8', '7', '6' };
    int[] result = CharArrayToIntArrayUtils.usingParseIntMethod(chars);

    assertArrayEquals(expected, result);
}