Convert Snake Case string to Camel Case in Java

Given a string in Snake Case, the task is to write a Java program to convert the given string from snake case to camel case and print the modified string.

Examples:

Input: str = “geeks_for_geeks” Output: GeeksForGeeks Input: str = “snake_case_to_camel_case” Output: SnakeCaseToCamelCase

Method 1: Using Traversal

1. The idea is to first capitalize the first letter of the string.
2. Then convert the string to string builder.
3. Then traverse the string character by character from the first index to the last index and check if the character is underscored then delete the character and capitalize the next character of the underscore.
4. Print the modified string.

Below is the implementation of the above approach: 

Java

// Java program for the above approach

import java.io.*;

class GFG {

    // Function to convert snake case
    // to camel case
    public static String
    snakeToCamel(String str)
    {
        // Capitalize first letter of string
        str = str.substring(0, 1).toUpperCase()
              + str.substring(1);

        // Convert to StringBuilder
        StringBuilder builder
            = new StringBuilder(str);

        // Traverse the string character by
        // character and remove underscore
        // and capitalize next letter
        for (int i = 0; i < builder.length(); i++) {

            // Check char is underscore
            if (builder.charAt(i) == '_') {

                builder.deleteCharAt(i);
                builder.replace(
                    i, i + 1,
                    String.valueOf(
                        Character.toUpperCase(
                            builder.charAt(i))));
            }
        }

        // Return in String type
        return builder.toString();
    }

    // Driver Code
    public static void
        main(String[] args)
    {

        // Given String
        String str = "geeks_for_geeks";

        // Function Call
        str = snakeToCamel(str);

        // Modified String
        System.out.println(str);
    }
}

Output:

GeeksForGeeks

Time Complexity: O(n) where n is the length of the string

Auxiliary Space: O(1)

Method 2: Using String.replaceFirst() method

1. The idea is to use String.replaceFirst() method to convert the given string from snake case to camel case.
2. First, capitalize the first letter of the string.
3. Run a loop till the string contains underscore (_).
4. Replace the first occurrence of a letter that present after the underscore to the capitalized form of the next letter of the underscore.
5. Print the modified string.

Below is the implementation of the above approach: 

Java

// Java program for the above approach

class GFG {

    // Function to convert the string
    // from snake case to camel case
    public static String
    snakeToCamel(String str)
    {
        // Capitalize first letter of string
        str = str.substring(0, 1).toUpperCase()
              + str.substring(1);

        // Run a loop till string
        // string contains underscore
        while (str.contains("_")) {

            // Replace the first occurrence
            // of letter that present after
            // the underscore, to capitalize
            // form of next letter of underscore
            str = str
                      .replaceFirst(
                          "_[a-z]",
                          String.valueOf(
                              Character.toUpperCase(
                                  str.charAt(
                                      str.indexOf("_") + 1))));
        }

        // Return string
        return str;
    }

    // Driver Code
    public static void
    main(String args[])
    {
        // Given string
        String str = "geeks_for_geeks";

        // Print the modified string
        System.out.print(snakeToCamel(str));
    }
}

Output:

GeeksForGeeks

Time Complexity: O(n) where n is the length of the string

Auxiliary Space: O(1)