Count uppercase letters in a string

justin :

I am trying to create a simple program that counts the uppercase characters in a String by looping through each character and incrementing an accumulator variable if the character is uppercase. Here is my code:

String str = "JuSTin"; //3 uppercase characters
int upperCaseCount = 0; //increment each time an uppercase character is encountered
char character; //the current character
for(int i = 0; i < str.length(); i++)
{
  character = str.charAt(i);
  System.out.println(character); //Log all characters to console just to see what is going on
  if(Character.isUpperCase(character))
      upperCaseCount++; 
  i++;  
}
System.out.println("Uppercase characters: " + upperCaseCount);

When ran this code outputs:

J
S
i
Uppercase characters: 2

What is causing this output? Where is the 'u' 'T' and 'n' in "JuSTin"? Why is upperCaseCount equal to 2 and not 3?

KeyMaker00 :

Just as a complement information (for your learning-purpose), you can solve it in different ways using:

• lambda,
• 'classic' for loop,
• loop construct introduced in Java 7,
• regular expression,
• or forEach loop

Each of these ways have their own advantages or drawbacks.

With a lambda

public static long countUpperCase(final String str) {
        return str
                .chars() // get all chars from the argument
                .filter(c -> Character.isUpperCase(c)) // filter only the uppercase
                .count(); // count the uppercase
    }

With a classic for loop

public static long countUpperCase(final String str) {
    long counter = 0;

    for(int i=0; i<str.length(); i++) {
        if(Character.isUpperCase(str.charAt(i))) {
            counter++;
        }
    }
    return counter;
}

With new loop construct (Java 7 or higher)

public static long countUpperCase(final String str) {
    long counter = 0;

    for(final char c: str.toCharArray()) {
        if(Character.isUpperCase(c)) {
            counter++;
        }
    }
    return counter;
}

There are already some explanation in other posts, e.g. Uppercase SO post

With a regular expression

public static long countUpperCase(final String str) {
    // \p{L} matches a single code point in the category "letter"
    // \p{L} matches all letters that are uppercase
    return str.split("(?=\\p{Lu})").length;
}

If you are interesting to dig a bit deeper, have a look at this interesting PDF: Guide to Regexp

With a forEach loop

public static long countUpperCase(final String str) {
    // the 'var' keyword can be used with Java 10 or higher
    final var counter = new AtomicInteger(0);

    // convert a string into a List<Character>
    // Note that this is only applicable since Java 8 or higher
    var chars = str
            .chars()
            .mapToObj(c -> (char) c)
            .collect(Collectors.toList());

    // count the number of uppercase letters
    chars.forEach(c -> {
        if(Character.isUpperCase(c)) {
            counter.incrementAndGet();
        }
    });

    return counter.get();
}