将字符串中的第一个字母大写。 我究竟做错了什么？

Question

What am I doing wrong? When I run my program it only prints some of my string, and it does not capitalize the first letter..

public class StringTraining extends ConsoleProgram {
    public void run() {
        String str = "halOOlOO";
        capitalize(str);
    }


    private String capitalize(String str){
        String s = "";
        char ch;
        for(int i = 0;i<str.length();i++) {
            ch = str.charAt(i);
            if(i==0 && Character.isLowerCase(ch)) {
                Character.toUpperCase(ch);
                s += ch;
                i++;
            } else {
                Character.toLowerCase(ch);
                s += ch;
                i++;
            }
        }
        println(s);
        return s;
    }

}

Answer 1

You need to assign the variable ch to the upper or lower case value:

for(int i = 0;i<str.length();i++) {
        ch = str.charAt(i);
        if(i==0 && Character.isLowerCase(ch)) {
            ch = Character.toUpperCase(ch);
            s += ch;
        } else {
            ch = Character.toLowerCase(ch);
            s += ch;
        }
    }

Answer 2

1. You should not increment i again in the loop since it will be done automatically in the signature of the loop.

2. You have to assign Character.toUpperCase(ch) to the String or append it.

3. I'd suggest you use a StringBuilder when looping to build a String object

---

Correction

private static String capitalize(String str){
    StringBuilder s = new StringBuilder();
    char ch;
    for(int i = 0;i<str.length();i++) {
        ch = str.charAt(i);
        if(i==0 && Character.isLowerCase(ch)) {
            s.append(Character.toUpperCase(ch));
        } else {
            s.append(Character.toLowerCase(ch));
        }
    }
    return s.toString();
}

Output

Halooloo

Answer 3

Remove some unnecessary codes from your capitalize(String) method such as i++ and use
s += String.valueOf(Character.toUpperCase(ch)); code instead of

Character.toUpperCase(ch);
s += ch;

Complete capitalize(String) method

private static String capitalize(String str) {
    String s = "";
    char ch;
    for (int i = 0; i < str.length(); i++) {
        ch = str.charAt(i);
        if (i == 0 && Character.isLowerCase(ch)) {
            s += String.valueOf(Character.toUpperCase(ch));
        } else {
            s += String.valueOf(Character.toLowerCase(ch));
        }
    }
    println(s);
    return s;
}

Answer 4

toLowerCase() return a string, you need to assign it to ch . You also need to increment your i only one time (in the for , and not in the if )

Answer 5

Change your capitalize(String str) method like this -

 private static String capitalize(String str) {
    char[] chars = str.toCharArray();
    String caps = chars[0]+"";
    caps = caps.toUpperCase();
    String output = caps;
    for(int i=1;i<chars.length;i++) {
        output = output + chars[i];
    }
    return output;
}

Output :

HalOOlOO