Sentence formatting

Question

I wrote this function to format a given sentence via Java, and I'm wondering if there is a better way of doing this without use of external libraries, such as with regex.

public class ChatFormat {

    public static void main(String[] args) {
        String input = "hello, it's a monday today and i think i'll go to the store. and get? some! tea.";
        System.out.println(optimizeText(input));
    }

    public static String optimizeText(String text) {
        char buf[] = text.toLowerCase().toCharArray();
        boolean endMarker = true;
        for (int i = 0; i < buf.length; i++) {
            char c = buf[i];
            if (endMarker && c >= 'a' && c <= 'z') {
                buf[i] = Character.toUpperCase(c);
                endMarker = false;
            }
            if (c == '.' || c == '!' || c == '?')
                endMarker = true;
            if (c == 'i') {
                char next = 0;
                if (i + 1 < buf.length) {
                    next = buf[i + 1];
                }
                char last = 0;
                if (i - 1 > 0)
                    last = buf[i - 1];
                if (last == ' ' && (next == ' ' || next == '\'' || next == 0))
                    buf[i] = Character.toUpperCase(c);
            }
        }
        return new String(buf, 0, buf.length);
    }
}

Answer 1

1. Inconsistent braces usage

Some of your if statements have enclosing { } but some do not, please standardize and use them throughout. :)

2. Character comparison

c >= 'a' && c <= 'z' can be better represented as Character.isLetter(c). IMHO it's easier to comprehend.

Similarly, last == ' ' and next == ' ' can be replaced with Character.isWhitespace(last) and Character.isWhitespace(next) respectively.

3. Derivation of next and last characters when encountering the letter 'i'

I'll prefer to use the ternary operator to set next and last as such, it's a little more compact:

char next = i < buf.length - 1 ? buf[i + 1] : 0;
char last = i > 1 ? buf[i - 1] : 0;

4. If-else-if ladder

Since your three if conditions are mutually exclusive, you can also consider putting them together in one if-else-if ladder, e.g.

if (endMarker && Character.isLetter(c)) {
    ...
} else if (c == '.' || c == '!' || c == '?') {
    ...
} else if (c == 'i') {
    ...
}

5. Use of toLowerCase()

Since you are already operating on a character array, perhaps you can consider converting to lower case letter as the final else branch, i.e.

char buf[] = text.toCharArray();
...
(for loop)
    if (...) {
        ...
    } else if (c == 'i') {
        ...
    } else {
        buf[i] = Character.toLowerCase(c);
    }

This does save one extra copy of the String in lower case, if anything.

6. Testing

It's fine so far to showcase one example using public static void main, but do consider building out some unit tests using a unit testing framework (e.g. TestNG, JUnit):

@Test // TestNG
public void doTest() {
    // Hamcrest matchers
    assertThat(optimizeText("that is its"), equalTo("That is its")); 
    assertThat(optimizeText("i'm"), equalTo("I'm"));
}

7. Other notes

Your simplified logic doesn't appear to handle sentence structures accurately, but since you seem to be more concerned with the formatting (capitalization), then I guess it's ok.