ReverseString.java

public class ReverseString {
    public static void main(String[] args) {
        String oldString = "abc1d2e fgh3i";
        String[] words = oldString.split(" ");
        String alphabet = "abcdefghijklmnopqrstuvwxyz";
        StringBuilder sentenceBuilder = new StringBuilder();

        for (String word : words) {
            StringBuilder wordBuilder = new StringBuilder();
            char[] unletterSymbols = new char[word.length()];

            for (int i = 0; i < word.length(); i++) {
                for (int j = 0; j < alphabet.length(); j++) {
                    if (word.charAt(i) == alphabet.charAt(j)) {
                        wordBuilder.append(word.charAt(i));
                        break;
                    }
                    if (j == alphabet.length() - 1) {
                        unletterSymbols[i] = word.charAt(i);
                    }
                }
            }
            wordBuilder.reverse();

            for (int i = 0; i < unletterSymbols.length; i++) {
                if (unletterSymbols[i] != 0) {
                    wordBuilder.insert(i, unletterSymbols[i]);
                }
            }

            sentenceBuilder.append(wordBuilder.toString())
                            .append(" ");
        }

        System.out.println(sentenceBuilder.toString());
    }
}