How to Count Specific Characters in a String in Java

Learn how to count specific characters in a string in Java using toCharArray(), for loop, and Java 8 Stream API . In this example, we count the occurrences of the character ‘h’ in each string.

Code Explanation point wise

  • Now the cd.test(‘h’, str) method passes the character ‘h’ and the string str as arguments.
  • The test(char c, String str) method counts the occurrences of ‘h’ in the string and returns the count.
  • After stores the returned count in the variable i.
  • Prints the total number of occurrences of ‘h’ using the toCharArray() method and a for loop.
  • The str.chars() method converts the string into an IntStream of character Unicode values.
  • Now .mapToObj(x -> (char) x) method converts each integer value into a Character object.
  • After .filter(ch -> ch == ‘h’) checks each character in the stream.
  • Keeps only the characters that are equal to ‘h’.
  • .count() counts all matching characters in the stream.
  • Returns the total number of occurrences of ‘h’.
  • Prints the count obtained using the Java 8 Stream API.
				
					public class CountCharDemo {

    public static void main(String[] args) {

        CountCharDemo cd = new CountCharDemo();
        String str = "how are you well here";

        // Using toCharArray() and for loop
        int i = cd.test('h', str);
        System.out.println("Total number of characters from toCharArray(): " + i);

        // Using Java 8 Stream API
        long count = str.chars()
                        .mapToObj(x -> (char) x)
                        .filter(ch -> ch == 'h')
                        .count();

        System.out.println("From Java 8 map and filter: " + count);
    }

    public int test(char c, String str) {

        int count = 0;

        char[] ch = str.toCharArray();

        for (int i = 0; i < ch.length; i++) {
            if (c == ch[i]) {
                count++;
            }
        }

        return count;
    }
}

Output :-
total number of character from TocharArray :- 2
from java8 map and filter :- 2

Count Character Frequency in a String in Java Using Java 8 Streams

				
					import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

public class CharacterFrequency {

    public static void main(String[] args) {

        String str = "how are you well here";

        Map<Character, Long> frequencyMap = str.chars()
                .mapToObj(ch -> (char) ch)
                .filter(ch -> ch != ' ')
                .collect(Collectors.groupingBy(
                        Function.identity(),
                        Collectors.counting()));

        frequencyMap.forEach((key, value) ->
                System.out.println(key + " = " + value));
    }
}

Output :
h = 2
o = 2
w = 2
a = 1
r = 2
e = 4
y = 1
u = 1
l = 2

Here are some related Java 8 programs that will help you understand Stream API concepts better:   

FAQ
How do you count a specific character in a string in Java?
You can count a character using a for loop, toCharArray(), or Java 8 Stream API methods such as filter() and count().
What does toCharArray() do in Java?
The toCharArray() method converts a string into a character array.
How can Java 8 Streams count characters?
Java 8 Streams use chars(), filter(), and count() to count matching characters efficiently.
What is the time complexity of counting characters in a string?
The time complexity is O(n) because each character is visited once.

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