String s="hi dude i                                 want apple";
    s = s.replaceAll("\\s+"," ");
    String[] split = s.split(" ");
    s="";
    for (int i = 0; i < split.length; i++) {
        split[i]=Character.toUpperCase(split[i].charAt(0))+split[i].substring(1);
        s+=split[i]+" ";
        System.out.println(split[i]);
    }
    System.out.println(s);

1. Java 8流

public static String capitalizeAll(String str) {
    if (str == null || str.isEmpty()) {
        return str;
    }

    return Arrays.stream(str.split("\\s+"))
            .map(t -> t.substring(0, 1).toUpperCase() + t.substring(1))
            .collect(Collectors.joining(" "));
}

例子:

System.out.println(capitalizeAll("jon skeet")); // Jon Skeet
System.out.println(capitalizeAll("miles o'Brien")); // Miles O'Brien
System.out.println(capitalizeAll("old mcdonald")); // Old Mcdonald
System.out.println(capitalizeAll(null)); // null

对于foo bAR到foo bAR，替换map()方法如下:

.map(t -> t.substring(0, 1).toUpperCase() + t.substring(1).toLowerCase())

2. 字符串()(Java 9+)

ublic static String capitalizeAll(String str) {
    if (str == null || str.isEmpty()) {
        return str;
    }

    return Pattern.compile("\\b(.)(.*?)\\b")
            .matcher(str)
            .replaceAll(match -> match.group(1).toUpperCase() + match.group(2));
}

例子:

System.out.println(capitalizeAll("12 ways to learn java")); // 12 Ways To Learn Java
System.out.println(capitalizeAll("i am atta")); // I Am Atta
System.out.println(capitalizeAll(null)); // null

3.Apache Commons文本

System.out.println(WordUtils.capitalize("love is everywhere")); // Love Is Everywhere
System.out.println(WordUtils.capitalize("sky, sky, blue sky!")); // Sky, Sky, Blue Sky!
System.out.println(WordUtils.capitalize(null)); // null

titlecase:

System.out.println(WordUtils.capitalizeFully("fOO bAR")); // Foo Bar
System.out.println(WordUtils.capitalizeFully("sKy is BLUE!")); // Sky Is Blue!

有关详细信息，请查看本教程。

Use:

    String text = "jon skeet, miles o'brien, old mcdonald";

    Pattern pattern = Pattern.compile("\\b([a-z])([\\w]*)");
    Matcher matcher = pattern.matcher(text);
    StringBuffer buffer = new StringBuffer();
    while (matcher.find()) {
        matcher.appendReplacement(buffer, matcher.group(1).toUpperCase() + matcher.group(2));
    }
    String capitalized = matcher.appendTail(buffer).toString();
    System.out.println(capitalized);

最基本和最简单的理解方法(我认为):

import java.util.Scanner;

public class ToUpperCase {
    static Scanner kb = new Scanner(System.in);

    public static String capitalize(String str){
        /* Changes 1st letter of every word 
           in a string to upper case
         */
        String[] ss = str.split(" ");
        StringBuilder[] sb = new StringBuilder[ss.length];
        StringBuilder capped = new StringBuilder("");
        str = "";

        // Capitalise letters
        for (int i = 0; i < ss.length; i++){
            sb[i] = new StringBuilder(ss[i]); // Construct and assign
            str += Character.toUpperCase(ss[i].charAt(0)); // Only caps
            //======================================================//

            // Replace 1st letters with cap letters
            sb[i].setCharAt(0, str.charAt(i)); 
            capped.append(sb[i].toString() + " ");  // Formatting
        }
        return capped.toString();
    }

    public static void main(String[] args){
        System.out.println(capitalize(kb.nextLine()));
    }
}

这里我们要实现单词的首字符大写

public static void main(String[] args) {
    String input ="my name is ranjan";
    String[] inputArr = input.split(" ");

    for(String word : inputArr) {
        System.out.println(word.substring(0, 1).toUpperCase()+word.substring(1,word.length()));
    }   
}

}

//输出:My Name Is Ranjan

有很多方法可以转换第一个大写单词的第一个字母。我有个主意。这很简单:

public String capitalize(String str){

     /* The first thing we do is remove whitespace from string */
     String c = str.replaceAll("\\s+", " ");
     String s = c.trim();
     String l = "";

     for(int i = 0; i < s.length(); i++){
          if(i == 0){                              /* Uppercase the first letter in strings */
              l += s.toUpperCase().charAt(i);
              i++;                                 /* To i = i + 1 because we don't need to add               
                                                    value i = 0 into string l */
          }

          l += s.charAt(i);

          if(s.charAt(i) == 32){                   /* If we meet whitespace (32 in ASCII Code is whitespace) */
              l += s.toUpperCase().charAt(i+1);    /* Uppercase the letter after whitespace */
              i++;                                 /* Yo i = i + 1 because we don't need to add
                                                   value whitespace into string l */
          }        
     }
     return l;
}