Problem

Given a string, the task is to capitalize the first character of each word in the string. A word is defined as a sequence of non-space characters. The function should return the resulting string with each word’s first character capitalized.

Examples

Example 1:

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 Input: "hello world"
 Output: "Hello World"
 Explanation: The first characters of both words 'hello' and 'world' are capitalized.

Example 2:

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 Input: "java is fun"
 Output: "Java Is Fun"
 Explanation: The first characters of the words 'java', 'is', and 'fun' are capitalized.

Example 3:

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Input: "k5kc is awesome!"
Output: "K5kc Is Awesome!"

Solution

Method 1 - Splitting around spaces and combining

A simple approach involves splitting the text by spaces to get an array of words. We then capitalize the first character of each word and append it, followed by a space, to a StringBuilder. Lastly, we convert the StringBuilder to a string and return it.

Code

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// Java program to capitalize first character of each word in a String
class Solution {
    public String capitalize(String str) {
        String[] words = str.split("\\s");
        StringBuilder sb = new StringBuilder();
 
        for (String word: words) {
            if (!word.isEmpty()) {
                sb.append(Character.toUpperCase(word.charAt(0)));
                sb.append(word.substring(1));
            }
            sb.append(" ");
        }
 
        // trim() to remove extra space in the end before returning
        return sb.toString().trim();
    }
 
    public static void main(String[] args)
    {
        String sentence = "k5kc is awesome!";
        String str = capitalize(sentence);
 
        System.out.println(str);
    }
}
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class Solution {
    // Method to capitalize first character of each word in the given text
    public String capitalizeFirstChar(String sentence) {
        return Pattern.compile("\\s")
                    .splitAsStream(sentence)
                    .map(this::capitalize)
                    .collect(Collectors.joining(" "));
    }

    // Helper method to capitalize the first character of a word
    public String capitalize(String s) {
        if (s.equals(""))
            return s;

        return s.substring(0, 1).toUpperCase() + s.substring(1);
    }
}
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class Solution {
    // Method to capitalize first character of each word in the given text
    public String capitalizeFirstChar(String sentence) {
        return Stream.of(sentence.split("\\s"))
                    .map(this::capitalize)
                    .collect(Collectors.joining(" "));
    }

    // Helper method to capitalize the first character of a word
    public String capitalize(String s) {
        if (s.equals(""))
            return s;

        return s.substring(0, 1).toUpperCase() + s.substring(1);
    }
}
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import org.apache.commons.lang3.text.WordUtils;

class Solution {
    public static void main(String[] args) {
        String sentence = "k5kc is awesome!";
        String str = WordUtils.capitalize(sentence);
 
        System.out.println(str);
    }
}
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We can also use Joiner class from Guava, along with Splitter and Iterables class, as demonstrated below:
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import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import com.google.common.collect.Iterables;

class Solution {
    // Method to capitalize first character of each word in the given text
    public String capitalizeFirstChar(String sentence) {
        return Joiner.on(' ')
                .join(Iterables.transform(Splitter.on(' ').split(sentence),
                                        this::capitalize));
    }

    // Helper method to capitalize the first character of a word
    public String capitalize(String s) {
        if (s.equals(""))
            return s;

        return s.substring(0, 1).toUpperCase() + s.substring(1);
    }
}
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class Solution:
    def capitalizeFirstChar(self, text: str) -> str:
        words = text.split()
        capitalized_words = [word.capitalize() for word in words]
        return ' '.join(capitalized_words)

Method 2 - Using Regex

We can also use regular expressions to capitalize the first letter of each word, as demonstrated below:

Code

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

class Solution {
    // Method to capitalize the first character of each word in the given text
    public String capitalizeFirstChar(String str) {
        StringBuffer sb = new StringBuffer();
        Matcher matcher = Pattern.compile("\\b(\\w)").matcher(str);

        while (matcher.find()) {
            matcher.appendReplacement(sb, matcher.group(1).toUpperCase());
        }

        matcher.appendTail(sb);
        return sb.toString();
    }
}
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import re

class Solution:
    # Method to capitalize the first character of each word in the given text
    def capitalizeFirstChar(self, text: str) -> str:
        return re.sub(r'\b\w', lambda x: x.group().upper(), text)