Subroutine Returns all Capitals on a String Paramter, Should only be first letter

Question

One of my problem sets requires me to take create a subroutine that will take a String variable as a parameter and return that same string except with the first letter of each word capitalized. The examples in the text use non-standard class the Professor specifically designed. I don't want to do this as I would think it makes more sense to learn with standard classes than see what else is out there. The problem I am having though is my subroutine is returning a String in all capitals. Here is my code:

import java.util.Scanner;

public class Capitalize {

static String capitalizeString(String x) {

    String completedConversion = "";

    for (int i=0; i < x.length(); i++) {

        if (i == 0) {
            char ch = x.charAt(i);
            ch = Character.toUpperCase(ch);
            completedConversion = completedConversion + ch;
            i++;
        }

        if (Character.isLetter(i - 1)) {

            char ch = x.charAt(i);
            completedConversion = completedConversion + ch;
         }

        else {

            char ch = x.charAt(i);
            ch = Character.toUpperCase(ch);
            completedConversion = completedConversion + ch;
        }

    }

    return completedConversion;

} // End of subroutine

I have not yet added any commenting etc. but it should be pretty straightforward.

SOLVED: Using Keammoort's answer

public class Capitalize {

    static String capitalizeString(String x) {

        String completedConversion = "";

        for (int i=0; i < x.length(); i++) {

            if (i == 0) {
                char ch = x.charAt(i);
                ch = Character.toUpperCase(ch);
                completedConversion = completedConversion + ch;
            }

            else if (!Character.isWhitespace(x.charAt(i - 1))) {

                char ch = x.charAt(i);
                completedConversion = completedConversion + ch;

            }

            else {

                char ch = x.charAt(i);
                ch = Character.toUpperCase(ch);
                completedConversion = completedConversion + ch;
            }

        }

return completedConversion;

Answer 1

Identifying the problem

This part code causes problems:

if (Character.isLetter(i - 1)) {
    char ch = x.charAt(i);
    completedConversion = completedConversion + ch;
} else {
    char ch = x.charAt(i);
    ch = Character.toUpperCase(ch);
    completedConversion = completedConversion + ch;
}

First of all method Character.isLetter() with parameter of type int returns true when passed parameter converted to a character (using codePoint) is a letter character. So for quite a few initial iterations you'll get a false. If Character.isLetter() returns false then you're changing a leter to uppercase anyway.

Getting actual character

I think there should be:

if (Character.isLetter(x.charAt(i - 1))) { //added getting character from input String
    char ch = x.charAt(i);
    completedConversion = completedConversion + ch;
} else {
    char ch = x.charAt(i);
    ch = Character.toUpperCase(ch);
    completedConversion = completedConversion + ch;
}

Using isWhitespace() instead of isLetter()

Even better: use isWhitespace() method. It will prevent situations when a digit is inside a word (then character after digit would be uppercase too).

if (!Character.isWhitespace(x.charAt(i - 1))) {
    //if previous char is not a whitespace don't change case
    char ch = x.charAt(i);
    completedConversion = completedConversion + ch;
} else {
    //if previous char is a whitespace change to uppercase
    char ch = x.charAt(i);
    ch = Character.toUpperCase(ch);
    completedConversion = completedConversion + ch;
}

Then all characters that are right after spaces, tabs, etc. will be uppercase.

Using a StringBuilder

Putting all this together plus using a StringBuilder to avoid creating many temporary Strings would be:

static String capitalizeString(String x) {
    StringBuilder completedConversion = new StringBuilder();

    for (int i = 0; i < x.length(); i++) {
        if (i == 0) {
            char ch = x.charAt(i);
            ch = Character.toUpperCase(ch);
            completedConversion.append(ch);
            i++;
        }

        if (!Character.isWhitespace(x.charAt(i - 1))) {
            char ch = x.charAt(i);
            completedConversion.append(ch);
        } else {
            char ch = x.charAt(i);
            ch = Character.toUpperCase(ch);
            completedConversion.append(ch);
        }

    }

    return completedConversion.toString();
}