Java Program to Count Words in String

You can count words in a string in Java by splitting the string with split("\\s+") and then getting the length of the resulting array, like int count = str.trim().split("\\s+").length;.

Examples

InputHello world

Output2

Input Java programming is fun

Output4

Input

Output0

How to Think About It

To count words in a string, first remove extra spaces at the start and end using trim(). Then split the string by spaces using split("\\s+") which divides the string wherever there is one or more spaces. The number of parts after splitting is the number of words.

Algorithm

1

Get the input string.

2

Remove leading and trailing spaces using trim.

3

Check if the string is empty after trimming; if yes, return 0.

4

Split the string by one or more spaces using split("\\s+").

5

Count the number of elements in the split array.

6

Return the count as the number of words.

Code

java

public class WordCount {
    public static void main(String[] args) {
        String str = "Java programming is fun";
        str = str.trim();
        if (str.isEmpty()) {
            System.out.println(0);
        } else {
            String[] words = str.split("\\s+");
            System.out.println(words.length);
        }
    }
}

Output

4

Dry Run

Let's trace the input "Java programming is fun" through the code

1

Input string

"Java programming is fun"

2

Trim spaces

"Java programming is fun" (no change)

3

Check if empty

Not empty, continue

4

Split by spaces

["Java", "programming", "is", "fun"]

5

Count words

4

6

Print result

4

Step	Words Array	Count
Split	["Java", "programming", "is", "fun"]	4

Why This Works

Step 1: Trim the string

Using trim() removes spaces at the start and end so they don't count as words.

Step 2: Split by spaces

Splitting by "\\s+" divides the string at one or more spaces, separating words.

Step 3: Count the words

The length of the split array is the total number of words in the string.

Alternative Approaches

Using StringTokenizer

java

import java.util.StringTokenizer;
public class WordCount {
    public static void main(String[] args) {
        String str = "Java programming is fun";
        StringTokenizer st = new StringTokenizer(str);
        System.out.println(st.countTokens());
    }
}

StringTokenizer is older and less flexible but simple for counting words separated by spaces.

Using Scanner

java

import java.util.Scanner;
public class WordCount {
    public static void main(String[] args) {
        String str = "Java programming is fun";
        Scanner sc = new Scanner(str);
        int count = 0;
        while (sc.hasNext()) {
            sc.next();
            count++;
        }
        sc.close();
        System.out.println(count);
    }
}

Scanner reads tokens separated by whitespace, useful for more complex input parsing.

Complexity: O(n) time, O(n) space

Time Complexity

The program scans the entire string once to split it, so time grows linearly with string length.

Space Complexity

Splitting creates an array of words, so space grows with the number of words in the string.

Which Approach is Fastest?

Using split is simple and fast for most cases; StringTokenizer and Scanner add overhead but offer more control.

Approach	Time	Space	Best For
split("\\s+")	O(n)	O(n)	Simple and fast word count
StringTokenizer	O(n)	O(n)	Legacy code or simple tokenization
Scanner	O(n)	O(n)	Complex input parsing with tokens