Java - convert camelCase to Sentence Case

In this article, we would like to show you how to convert camelCase to sentence case in Java.

1. Simple solution

In this example, we use some string methods to convert camelCase to Sentence Case such as:

• replaceAll() with regex - to replace each capital letter with the same letter preceded by space character,
• substring(0, 1) - to get only the first letter from the string,
• substring(1) - to add whole string except the first character,
• toUpperCase() - to convert letters to upper case.

public class Example {

    static Object sentenceCase(String text) {
        if (!text.equals("")) {
            String result = text.replaceAll("([A-Z])", " $1");
            return result.substring(0, 1).toUpperCase() + result.substring(1).toLowerCase();
        }
        return null;
    }

    public static void main(String[] args) {
        String text = "mySampleText";
        System.out.println(sentenceCase(text));  // My sample text
    }
}

2. Optimal solution

This example present more complex but optimal solution.

When we want to reduce the number of compile function calls of the pattern class, we can explicitly create a pattern and then perform matcher and replaceAll() on it.

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Example {

    static final Pattern CAPITAL_LETTER_PATTERN = Pattern.compile("([A-Z])");

    static Object sentenceCase(String text) {
        if (text == null || text.isEmpty()) {
            return text;
        }
        Matcher matcher = CAPITAL_LETTER_PATTERN.matcher(text);
        String result = matcher.replaceAll(" $1");
        return result.substring(0, 1).toUpperCase() + result.substring(1).toLowerCase();
    }

    public static void main(String[] args) {
        String text = "mySampleText";
        System.out.println(sentenceCase(text));  // My sample text
    }
}