Java Programs›Strings›Count Special Characters in a String

Count Special Characters in a String in Java

beginner· Strings · String

Problem

A special character is anything that isn't a letter, digit, or whitespace — punctuation and symbols like @, #, or !.

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

Input

Hello@World#2024!

Output

Special characters: 3

Java Program

Java

public class CountSpecialCharacters {
    public static void main(String[] args) {
        String str = "Hello@World#2024!";
        int count = 0;
        for (char c : str.toCharArray()) {
            // Anything that isn't a letter/digit or whitespace counts as special
            if (!Character.isLetterOrDigit(c) && !Character.isWhitespace(c)) count++;
        }
        System.out.println("Special characters: " + count);
    }
}

▶ Run Code

Output

Special characters: 3

Core Logic

Defining a special character as 'everything that's left over' after ruling out letters, digits, and whitespace makes the check a single condition.

How It Works

1A for-each loop visits each character of the string in turn.
2Character.isLetterOrDigit(c) rules out ordinary letters and numbers.
3Character.isWhitespace(c) rules out spaces, tabs, and newlines.
4Anything that fails both checks — punctuation and symbols — increments the count variable.

For "Hello@World#2024!", the scan finds three special characters: @, #, and !.

💡

Key Point: Defining 'special' by exclusion — not a letter, not a digit, not whitespace — avoids having to list out every possible punctuation mark or symbol individually.

Complexity

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

Why: Each character is checked once against isLetterOrDigit() and isWhitespace(), with only a running counter kept regardless of string length.

Key Concepts

Character.isLetterOrDigit()Character.isWhitespace()for-each loop

Approach 2: Java 8

Java

public class CountSpecialCharactersStream {
    public static void main(String[] args) {
        String str = "Hello@World#2024!";
        // Keeps characters that are neither a letter/digit nor whitespace
        long count = str.chars()
            .filter(c -> !Character.isLetterOrDigit(c) && !Character.isWhitespace(c))
            .count();
        System.out.println("Special characters: " + count);
    }
}

▶ Run Code

Output

Special characters: 3

Core Logic

The same 'everything left over' definition can filter a stream of character codes down to just the special characters, then count what's left.

How It Works

1str.chars() returns an IntStream of the string's character codes.
2.filter(c -> !Character.isLetterOrDigit(c) && !Character.isWhitespace(c)) keeps only characters that are neither a letter/digit nor whitespace.
3.count() reduces the filtered stream down to a single long total.

Filtering "Hello@World#2024!" keeps only @, #, and !, so count() returns 3.

💡

Key Point: The filter condition is the exact same boolean expression the loop version checks — the stream just changes how it's applied across the string.

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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