如何在java中使字符串的第一个字母大写？[已关闭]

public class CapitalizeFirstLetter {
    public static String capitalizeFirstLetter(String str) {
        if (str == null || str.isEmpty()) {
            return str;
        }
        return str.substring(0, 1).toUpperCase() + str.substring(1);
    }

    public static void main(String[] args) {
        String input = "hello world";
        String result = capitalizeFirstLetter(input);
        System.out.println(result); // 输出: Hello world
    }
}

import org.apache.commons.lang3.StringUtils;

public class CapitalizeFirstLetter {
    public static void main(String[] args) {
        String input = "hello world";
        String result = StringUtils.capitalize(input);
        System.out.println(result); // 输出: Hello world
    }
}

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
</dependency>

import java.util.Optional;

public class CapitalizeFirstLetter {
    public static String capitalizeFirstLetter(String str) {
        return Optional.ofNullable(str)
                       .map(s -> s.substring(0, 1).toUpperCase() + s.substring(1))
                       .orElse(str);
    }

    public static void main(String[] args) {
        String input = "hello world";
        String result = capitalizeFirstLetter(input);
        System.out.println(result); // 输出: Hello world
    }
}