How to convert a string to uppercase without using the toUpperCase method?

Question

I'm a beginner at java and can't get this code to work. What I have to do is convert any inputted string to uppercase without using the toUpperCase string method. This is what I have:

public String toUpperCase(String str)
{
    for(int i = 0; i < str.length(); i++)
    {
        char a = str.charAt(i);
        a = Character.toUpperCase(a);
        str += Character.toString(a);
    }
return str;
}

Answer 1

You are using str as input, and output (so your String has infinite length, as you keep adding characters). And you can use static, because you aren't using instance state. And, you might use a for-each loop. Finally, add another String, or better a StringBuilder like

public static String toUpperCase(String str) {
    StringBuilder sb = new StringBuilder();
    for (char ch : str.toCharArray()) {
        sb.append(Character.toUpperCase(ch));
    }
    return sb.toString();
}