Thread: Find the longest word in string - code has bugs

I am writing the following code to display the longest word in a sentence and there are bugs which I have no idea how to solve this. Please help me.

Input st = aaaa bbbb ccccc ddd eee ffff aaaa bbbb ccccc ddd eee ffff aaaa bbbb ccccc ddd eee ffff
Output = remaining: ddd eee ffff

If it is a shorter sentence, the code works fine.
Input st = aaaa bbbb ccccc ddd eee ffff aaaa bbbb
Output = longest: ccccc

public static void charNum(String st) {
		String first_word;
		int word_length;
		String longest_word = "";
		int temp_wordcount = 0;
		String remaining_words = "";
 
		for (int i = 0; i < st.length(); i++) {
 
			word_length = st.indexOf(' '); 
			if (word_length<0) {
				break;
			}
			first_word = st.substring(0, word_length); 
			remaining_words = st.substring(word_length+1, st.length()); 
			if (word_length > temp_wordcount) {
				longest_word = first_word;
			}
			temp_wordcount = longest_word.length();
			st = st.substring(word_length+1);
		}
 
		if (remaining_words.length() > longest_word.length()) {
			System.out.println("remaining: " + remaining_words);
		}
		else {
			System.out.println("longest: " +longest_word); 
		}

Originally Posted by Norm

Can you describe in English the steps the code needs to take to solve the problem?
Normally I can read the comments in code to see what it is trying to do and how it is going to do it, but the posted code has no comments.

What is the expected output from the code?

Hi Norm,
Thank you for your reply. I have added the comments below and hope it makes it more clear.
The expected output from the code is to display the longest word in sentence. The problem is that it works fine for shorter sentence. But for longer sentence it leaves out the last few words. For example:

Shorter sentence - it works fine to display the longet word in the sentence.
Input: Returns the char value at the specified index.
Output: longest: specified

Longer sentence - it displays the last few words in the sentence
Input: If the char value specified at the given index is in the high-surrogate range, the following index is less than the length of this String, and the char value at the following index is in the low-surrogate range, then the supplementary code point corresponding to this surrogate pair is returned.
Output: longest: to this surrogate pair is returned.

/** Method displays the longest word in a sentence**/
public static void charNum(String st) { //takes in a string st as parameter
                // define variables
		String first_word;
		int word_length;
		String longest_word = "";
		int temp_wordcount = 0;
		String remaining_words = "";
 
                // loop throgh the input string st
		for (int i = 0; i < st.length(); i++) {
			word_length = st.indexOf(' '); // find the index of the first space in string and store it in variable word_length 
			if (word_length<0) { // the last word has no space at the end and index of space is -1
				break;
			}
			first_word = st.substring(0, word_length);  // extract the first word of the input string from index 0 to the first space and store it in variable first_word
			remaining_words = st.substring(word_length+1); // remove the first word from the string. The remaining words in string is stored in variable remaining_words
			if (word_length > temp_wordcount) { // if number of characters of the first word is greater than the number of characters of the longest word , first word becomes the longest word stored in variable longest_word
				longest_word = first_word;
			}
			temp_wordcount = longest_word.length(); // replace the number of characters of the longest word 
			st = remaining_words; // first word of string is removed and stored in parameter st
		}
                // the loop does not account for the last word of the string because there is no space after the last word 
		if (remaining_words.length() > longest_word.length()) { // if the number of characters in last word of string is greater than variable longest_word from the loop, display the last word. Otherwise, display longest_word 
			System.out.println("longest: " + remaining_words);
		}
		else {
			System.out.println("longest: " +longest_word); 
		}

Originally Posted by Norm

What is all that about? This description contains lots of terms that require some definitons:
Can you explain what high-surrogate and low-surrogate range means?
How is the index computed? What is in it?
What is the following index? How is it computed?
What is supplementary code point? Why is it returned?

This is just the input sentence for the code to find the longest word. The meaning of it does not matter, which you can replace it with any other sentences. This is a sentence I copied from the oracle doc. My point is that the code works when the sentence is short but not long sentence.

Originally Posted by Norm

Why is the code that saves the current longest word separated from the code that saves the length of the current longest word? Either put them together or get rid of the separate length variable and just use the .length() method to get the length of the current longest word.

Which line of code are you referring to please?

Originally Posted by Norm

How are you debugging the code? Add some print statements that show the values of the variables as they are used and changed.

I have printed every single line of code but still do not understand why the for loop stops and leaves the last few words of a long sentence. Just hope I can get some help here.

Originally Posted by Norm

Can you copy and paste here the contents of the printed out values of the variables used in the code?
There will be a clue in the printed values that will help you solve the problem.

This is my revised code:

public static void charNum(String st) {
		// define variables
		String first_word;
		int word_length;
		String longest_word = "";
		int temp_wordcount = 0;
		String remaining_words = "";
 
		for (int i = 0; i < st.length(); i++) {
			System.out.println("1. sentence: " + st);
 
			word_length = st.indexOf(' '); // find the index of the first space in string and store it in variable word_length 
			System.out.println("2. number of characters: " + word_length);
 
			if (word_length<0) {// the last word has no space at the end and index of space is -1
				break;
			}
			first_word = st.substring(0, word_length); // extract the first word of the input string from index 0 to the first space and store it in variable first_word
			System.out.println("3. first word: " + first_word);
 
			remaining_words = st.substring(word_length+1); // remove the first word from the string. The remaining words in string is stored in variable remaining_words
			System.out.println("4. remaining sentence: "+remaining_words);
 
			if (word_length > longest_word.length()) { // if number of characters of the first word is greater than the number of characters of the longest word , first word becomes the longest word stored in variable longest_word
 
				longest_word = first_word;
			}
			System.out.println("5. longest word: "+longest_word);
 
			st = remaining_words; // first word of string is removed and stored in parameter st
			System.out.println("message: " + st + "\n--------------------------");
		}
                // the loop does not account for the last word of the string because there is no space after the last word 
		if (remaining_words.length() > longest_word.length()) { // if the number of characters in last word of string is greater than variable longest_word from the loop, display the last word. Otherwise, display longest_word 
			System.out.println("remaining: " + remaining_words);
		}
		else {
			System.out.println("longest: " +longest_word); 
		}

The output is very long. At the end of the output, the loop stops at the last 3 words.
Output:

1. sentence: A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 1
3. first word: A
4. remaining sentence: digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: A
message: digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 7
3. first word: digital
4. remaining sentence: computer stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: digital
message: computer stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: computer stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 8
3. first word: computer
4. remaining sentence: stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: computer
message: stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: stores information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 6
3. first word: stores
4. remaining sentence: information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: computer
message: information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: information as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 11
3. first word: information
4. remaining sentence: as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: as numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 2
3. first word: as
4. remaining sentence: numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: numbers (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 7
3. first word: numbers
4. remaining sentence: (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: (1234). A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 7
3. first word: (1234).
4. remaining sentence: A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: A digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 1
3. first word: A
4. remaining sentence: digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: digital computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 7
3. first word: digital
4. remaining sentence: computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: computer stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 8
3. first word: computer
4. remaining sentence: stores information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: stores information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: stores information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 6
3. first word: stores
4. remaining sentence: information as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: information as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: information as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 11
3. first word: information
4. remaining sentence: as numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: as numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: as numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 2
3. first word: as
4. remaining sentence: numbers (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: numbers (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: numbers (1234). A digital computer stores information as numbers (1234).
2. number of characters: 7
3. first word: numbers
4. remaining sentence: (1234). A digital computer stores information as numbers (1234).
5. longest word: information
message: (1234). A digital computer stores information as numbers (1234).
--------------------------
1. sentence: (1234). A digital computer stores information as numbers (1234).
2. number of characters: 7
3. first word: (1234).
4. remaining sentence: A digital computer stores information as numbers (1234).
5. longest word: information
message: A digital computer stores information as numbers (1234).
--------------------------
1. sentence: A digital computer stores information as numbers (1234).
2. number of characters: 1
3. first word: A
4. remaining sentence: digital computer stores information as numbers (1234).
5. longest word: information
message: digital computer stores information as numbers (1234).
--------------------------
1. sentence: digital computer stores information as numbers (1234).
2. number of characters: 7
3. first word: digital
4. remaining sentence: computer stores information as numbers (1234).
5. longest word: information
message: computer stores information as numbers (1234).
--------------------------
1. sentence: computer stores information as numbers (1234).
2. number of characters: 8
3. first word: computer
4. remaining sentence: stores information as numbers (1234).
5. longest word: information
message: stores information as numbers (1234).
--------------------------
1. sentence: stores information as numbers (1234).
2. number of characters: 6
3. first word: stores
4. remaining sentence: information as numbers (1234).
5. longest word: information
message: information as numbers (1234).
--------------------------
1. sentence: information as numbers (1234).
2. number of characters: 11
3. first word: information
4. remaining sentence: as numbers (1234).
5. longest word: information
message: as numbers (1234).
--------------------------
remaining: as numbers (1234).

Originally Posted by Norm

Why did the loop stop? Look at the values control the looping: i and st.length() What were their values at the end of each loop?

I found the problem now. This is the output of i and st.length()
i: 0
st.length(): 168
=================
i: 1
st.length(): 160
=================
i: 2
st.length(): 151
=================
i: 3
st.length(): 144
=================
i: 4
st.length(): 132
=================
i: 5
st.length(): 129
=================
i: 6
st.length(): 121
=================
i: 7
st.length(): 113
=================
i: 8
st.length(): 111
=================
i: 9
st.length(): 103
=================
i: 10
st.length(): 94
=================
i: 11
st.length(): 87
=================
i: 12
st.length(): 75
=================
i: 13
st.length(): 72
=================
i: 14
st.length(): 64
=================
i: 15
st.length(): 56
=================
i: 16
st.length(): 54
=================
i: 17
st.length(): 46
=================
i: 18
st.length(): 37
=================
i: 19
st.length(): 30
=================
i: 20
st.length(): 18
=================
remaining: as numbers (1234).

At the end of the loop,
i: 20
st.length(): 18

Now i > st.length() and that's why the loop stops looping. And there are a few words left in the sentence to be looped. That is why this code does not work for longer sentences.
So is there any idea how I can solve this problem please?

Originally Posted by Norm

The value in i continues to increase as the length of st decreases.

Don't use i and st.length to control the loop. The value in i is never used in the loop so it is not needed.
What other condition can be used to end the loop?
The code has a break statement that will end the loop. Can that be used?
If so write an infinite loop with while(true) and get rid of the for statement.

Yes a while loop fixes the problem! Thank you so much Norm!