'From snake_case to camelCase in Java

Can anyone tell me how to convert a string in snake_case as: 

camel_case

to a string in camelCase as:

camelCase

in Java?

Thank you in advance.

javastring


Solution 1:[1]

Also Guava's CaseFormat offers quite a neat solution that allows you to transform from and to camel case and even other specific cases.

CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, "camel_case"); // returns camelCase
CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, "CAMEL_CASE"); // returns CamelCase
CaseFormat.LOWER_CAMEL.to(CaseFormat.UPPER_UNDERSCORE, "camelCase"); // returns CAMEL_CASE
CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_HYPHEN, "CamelCase"); // returns camel-case

Solution 2:[2]

You can use toCamelCase util:

CaseUtils.toCamelCase("camel_case", false, new char[]{'_'}); // returns "camelCase"

from Apache Commons Text.

Solution 3:[3]

This might be pretty, and it works

public class Test {

    public static void main(String[] args) {
        String phrase = "always_use_camel_back_notation_in_java";
        while(phrase.contains("_")) {
                phrase = phrase.replaceFirst("_[a-z]", String.valueOf(Character.toUpperCase(phrase.charAt(phrase.indexOf("_") + 1))));
            }
            System.out.println(phrase);
        }
    }

Solution 4:[4]

This isn't pretty, but it works:

String phrase = "camel_case";
String[] words = phrase.split("_");
String newPhrase = words[0];
for(int i=1; i<words.length; i++){
  newPhrase += words[i].substring(0,1).toUpperCase() + words[i].substring(1);
}

Solution 5:[5]

Take a look at oracle's documentation for the string class, notably substring, charAt, indexOf, and toUpperCase

(You can use these as puzzle pieces to solve your problem)

Solution 6:[6]

Using split("_") and looping over those parts is one way to do it.

Here is an alternative using a StringBuilder. 

String s = "make_me_camel_case";
StringBuilder sb = new StringBuilder(s);

for (int i = 0; i < sb.length(); i++) {
    if (sb.charAt(i) == '_') {
        sb.deleteCharAt(i);
        sb.replace(i, i+1, String.valueOf(Character.toUpperCase(sb.charAt(i))));
    }
}

System.out.println(sb.toString()); // makeMeCamelCase

Solution 7:[7]

Java SE 8+

Using Java-8 Stream API, we can do it in a single statement.

import java.util.Arrays;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        String str = "snake_case_to_camel_case";

        str = str.indexOf("_") != -1
                ? str.substring(0, str.indexOf("_")) + 
                    Arrays.stream(str.substring(str.indexOf("_") + 1).split("_"))
                        .map(s -> Character.toUpperCase(s.charAt(0)) + s.substring(1)).collect(Collectors.joining())
                : str;

        System.out.println(str);
    }
}

Output:

snakeCaseToCamelCase

ONLINE DEMO

Java SE 9+

Matcher#replaceAll?(Function<MatchResult, String> replacer) introduced with Java SE 9, makes it further easy.

import java.util.regex.Pattern;

public class Main {
    public static void main(String[] args) {
        String str = "snake_case_to_camel_case";

        str = Pattern.compile("_([a-z])")
                    .matcher(str)
                    .replaceAll(m -> m.group(1).toUpperCase());

        System.out.println(str);
    }
}

Output:

snakeCaseToCamelCase

ONLINE DEMO

Solution 8:[8]

import org.apache.commons.lang3.text.WordUtils;

public String snakeToCamelCase(String snakeWord) {
    String camelWord = snakeWord.replaceAll("_", " ");
    camelWord = WordUtils.capitalizeFully(camelWord);
    return camelWord.replaceAll(" ", "");
}

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 Alex
Solution 2 Community
Solution 3 Roee Gavirel
Solution 4 pdem
Solution 5 Noam Hacker
Solution 6 OneCricketeer
Solution 7
Solution 8

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