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Count Spaces in a String in Java

beginner· Strings · String

Problem

Counting spaces means counting how many whitespace characters — most commonly the space character — appear in a string.

Given a string, count how many space characters it contains.

Input

Java is a powerful language

Output

Spaces: 4

Java Program

Java

public class CountSpaces {
    public static void main(String[] args) {
        String str = "Java is a powerful language";
        int count = 0;
        for (char c : str.toCharArray()) {
            if (c == ' ') count++; // counts the literal space character only
        }
        System.out.println("Spaces: " + count);
    }
}

▶ Run Code

Output

Spaces: 4

Core Logic

A single pass through the string, comparing each character directly against a space, tallies every one found.

How It Works

1A for-each loop visits each character of the string in turn.
2c == ' ' checks whether the current character is exactly the space character.
3A match increments the count variable; anything else is skipped.
4After the loop, count holds the total number of spaces found.

For "Java is a powerful language", the five words are separated by four spaces, so count ends at 4.

💡

Key Point: This checks only the literal space character — tabs or newlines wouldn't be counted, unlike Character.isWhitespace(), which treats any whitespace as a match.

Complexity

Time Complexity: O(n)Space Complexity: O(1)

Why: Each character is visited once, and only a single running counter is kept regardless of string length.

Key Concepts

char comparisonfor-each loopcounter variable

Approach 2: Java 8

Java

public class CountSpacesStream {
    public static void main(String[] args) {
        String str = "Java is a powerful language";
        // filter() keeps only the space character codes; count() reduces to a single total
        long count = str.chars().filter(c -> c == ' ').count();
        System.out.println("Spaces: " + count);
    }
}

▶ Run Code

Output

Spaces: 4

Core Logic

The same character comparison can filter a stream of character codes down to just the spaces, then count what's left.

How It Works

1str.chars() returns an IntStream of the string's character codes.
2.filter(c -> c == ' ') keeps only the codes matching the space character.
3.count() reduces the filtered stream down to a single long total.

Filtering "Java is a powerful language" keeps only the four space characters, so count() returns 4.

💡

Key Point: Swapping the lambda to Character::isWhitespace instead of c == ' ' would extend this to catch tabs and newlines too, the same trade-off the loop version has.

Complexity

Time Complexity: O(n)Space Complexity: O(1)

Why: The stream still visits every character once, and count() reduces straight down to a single long without collecting anything.

Key Concepts

Streamchars()filter()count()

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