Need help reading through my String to push to Stack

Question

Hello and thank you for reading. I have written a program to reverse the words in a string using a stack. I am to use 3 sentences and reverse each sentence separately. I have been able to reverse the entire string, which wasn't an issue. Then I changed my program so I am reading to the period and reversing the first sentence. However, I can't get it to read the next sentence. I believe I need a second loop but this is where I struggle. There are several questions/answers on this site that address this assignment, but none that have really taken the approach I have so they aren't relevant. At least, not from what I can tell. This is what I have:

for (String word : wordArray) {
    if (word.endsWith(".") {
        Stack.push(word.substring(0, word.length()-1));
        break;
    }
    else {
        Stack.push(word);
    }
}

So my sentences are: "Cats are cool. Dogs are cool. So are turtles." My program will print: "cool are Cats" I know I need to append a period and I can figure that out later. I'm just struggling with how to create a second loop to continue reading the rest of the string. What I need is: "cool are Cats. cool are Dogs. turtles are So."

Answer 1

You were thinking in the right direction: you do need one more loop to empty out the stack when the end of a sentence has been encountered, and you need some mean of storing the data (it could be an ArrayList, or a StringBuilder).

I would use a StringBuilder to store reversed sentences.

The logic of generating a reversed sentence by retrieving the elements from the stack can be extracted into a separate method. In a nutshell, it's while-loop that runs until the stack is not empty. To join the string back into a sentence, I would use a StringJoiner which facilitates combining the strings using a specified delimiter (feel free to reimplement this logic as you see fit, the point of this answer is to explain the algorithm and provide a source of inspiration rather than be a ready to go copy-past solution, for instance, you can use two StringJoiners instead of the combination StringJoiner + StringBuilder, I've only shown one possibility).

That's how it might be implemented:

public static String reverseSentences(String[] wordArray) {
    Stack<String> stack = new Stack<>();
    StringBuilder reversedSentences = new StringBuilder();
    
    for (String word : wordArray) {
        if (word.endsWith(".")) {
            
            stack.push(word.substring(0, word.length() - 1));
            
            reversedSentences
                .append(createSentence(stack)) // appending the reversed sentence
                .append(". ");                 // adding a period and a white space at the end of the sentence

        } else {
            stack.push(word);
        }
    }
    return reversedSentences.toString();
}

public static String createSentence(Stack<String> stack) {
    StringJoiner sentence = new StringJoiner(" "); // white space would be used a delimiter between the words
    while (!stack.isEmpty()) {
        sentence.add(stack.pop());
    }
    return sentence.toString();
}

main()

public static void main(String[] args) {
    System.out.println(reverseSentences("Cats are cool. Dogs are cool. So are turtles.".split(" ")));
}

Output:

cool are Cats. cool are Dogs. turtles are So.