Question

I am practicing some exercises for my CS final, and am stuck on this problem, where I have to read a string, get a minimum length from the user, and return the amount of words that have at least that many letters. It seems as if my code is fine, but it can’t print out the answer. Can anyone help me out?

public class WordCount {



    public static void main (String [] args) {
        System.out.println("Enter a string: "); 
        String input =  IO.readString();


        System.out.println("Enter minimum word length");
        int wordlength = IO.readInt();
        int count = 0 ;
        do  {

            for (int i = 0 ; i < input.length(); i ++) {

                if (input.indexOf(i) == ' ') {

                    String check = input.substring(0, i);
                    if (check.length() >= wordlength) {

                        count++;
                        input = input.substring(i);
                        break;

                    }
                }

                    }

        } while (input.length() > 0);


    System.out.print("Words longer than " + wordlength + " characters: " + count);

    }

}

It seems as if the while loop runs infinitely, but I can’t figure out why!

Answer 1

Currently there are few problems with your code that I’ll point out first: –

if (input.indexOf(i) == ' ')

In the above statement, you should use String#charAt method, to get a character at a particular index. String#indexOf method is used for reverse process, i.e, you have a character and you want to find it’s index.

Secondly, you are modifying your input inside the loop itself. And you are using the length of input in the terminating condition in the loop. You should not do anything like this.
Rather, you can use another variable, which will store the index of last word you processed. And use that index in your substring method.

Thirdly, you don’t really need a do while loop here. Your for loop itself is iterating over all your characters. Just remove the break from your if, which is really not required.

So, your code will be modified to this: –

int oldIndex = 0;  // to maintain the end index of previous word.
int length = input.length();
for (int i = 0 ; i < length; i ++) {

          if (input.charAt(i) == ' ' || i == length - 1) {

                // If the word is at the end, then probably your first 
                // condition in above `if` would fail, that is why I used a 
                // second condition, which checks the end of string

                // Now for the end of the string, we would need to use a single
                // arguement substring method to get the word till the end.
                // hence the below conditional expression.

                String check = (i == length - 1)? input.substring(oldIndex): 
                                                input.substring(oldIndex, i);

                oldIndex = i + 1;  // Set oldIndex to the next index.

                if (check.length() >= wordlength) {

                    count++;
                    //  input = input.substring(i);  Don't do this
                    // break;   // Don't break too.

                }
           }

}

---

Now this was the modification of your code, so that you can learn what was your mistake.

However, you have a pretty easy way to get what you want. You can use String#split method to split your string on space, which will return you an array of all the words, and you can operate on those words.

It works something like this (in case you can use it): –

String[] words = input.split(" ");  // split input string on space

for (int i = 0; i < words.length; i++) {  // iterate over array
    if (words[i].length() >= wordLength) {
        count++;
    }
}

System.out.println(count);