How to capitalize the first character of a string in Android?

I understand that there is no such function in native Java.

Since it's something as simple as what you mention in your algorithm, I don't know if it's worth relying on a library or the like to do that. The implementation I came up with in particular is very similar to yours. Only that it is using substringand also contemplating the null string. More or less the following:

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

I hope the answer is useful.

Greetings.

To complement @hdlopez's answer, this process should be very simple, the most common would be this function (which includes a validation) where we require to change the first letter to uppercase:

public static String ucFirst(String str) {
  if (str == null || str.isEmpty()) {
    return "";            
  } else {
    return str.substring(0, 1).toUpperCase() + str.substring(1); 
  }
}

Android is trying not to use the Apache libraries, as happened with the Http class and external libraries to do this, I don't see an option for something so simple.

Another option to ensure always having the first character in uppercase and the others in lowercase is:

public static String ucFirst(String str) {
  if (str == null || str.isEmpty()) {
    return "";            
  } else {
    return  Character.toUpperCase(str.charAt(0)) + str.substring(1, str.length()).toLowerCase();
  }
}

Example:

String ciudad = ucFirst("barcElonA"); 

the city value would be:Barcelona

There are several answers on Stackoverflow on this topic: https://stackoverflow.com/questions/15259774/capitalise-first-letter-in-string-android

Apache Commons Lang has a method called StringUtilscapitalize(String) that does exactly that. It also has many other methods, you would have to evaluate if adding an extra 2MB to the APK is worth it. . Add about 400KB to your apk.

If you want to do it in a single line, you can resort to something like this, which doesn't have the if, and is easier to read:

String resultado = cadena.substring(0,1).toUpperCase() + cadena.substring(1);

But this method is probably less efficient than the one in your example.

Keep in mind that if the string is empty/null, an exception will have to be handled. Or use a defensive approach that includes a null/void validation before executing the statement, it will depend on the use case and adding it already removes it from a single line.

I don't think it's recommended to include a library just for capitalization because the process is quite simple, but we have this:

String texto = "hola mundo";

No library, using String and Character .

texto = Character.toUpperCase(texto.charAt(0)) + texto.substring(1,texto.length());

Without library, with lambdas (Java 8) [ Source ]

texto = IntStream.concat(IntStream.of(texto.codePointAt(0)).map(Character::toUpperCase), texto.codePoints().skip(1) ).collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append).toString();

With library, Apache Commons Lang - WordUtils [ API ]

texto = WordUtils.capitalize(texto);

The capitalize(...) method of StringUtils is based on the same algorithm as that of WordUtils.

texto = StringUtils.capitalize(texto);

I made a similar answer and they gave me this answer. it worked perfect for me.

public static String convierte(String string) {
    if (string == null) {
        return null;
    }
    StringBuilder builder = new StringBuilder();
    StringTokenizer st = new StringTokenizer(string," ");
    while (st.hasMoreElements()) {
        String ne = (String)st.nextElement();
        if (ne.length()>0) {
            builder.append(ne.substring(0, 1).toUpperCase());
            builder.append(ne.substring(1).toLowerCase()); //agregado
            builder.append(' ');
        }
    }
    return builder.toString();
}