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How to count the number of occurrences of a char in a String?

This example show you how to count the number of a character occurrences in a string. We show two ways to do it, using the String.replaceAll(String regex, String replace) method and creating a loop that check every char in the String and count the matched char.

package com.javacoderanch.example.lang;

public class CharCounter {
    public static void main(String[] args) {
        String text = "a,b,c,c,e,f,g,g,g,g,h";

        //
        // Use the CharCounter.countCharOccurrences() method to count.
        //
        int numberOfLetterC = CharCounter.countCharOccurrences(text, 'c');
        System.out.println("Letter c = " + numberOfLetterC);

        //
        // Other solution is to use the String.replaceAll() method. We'll
        // replace the chars other than the counted char with an empty string.
        // To get the char occurrences we count the lenght of the remaining
        // string.
        //
        int numberOfComma = text.replaceAll("[^,]", "").length();
        System.out.println("Comma    = " + numberOfComma);

        int numberOfLetterG = text.replaceAll("[^g]", "").length();
        System.out.println("Letter g = " + numberOfLetterG);
    }

    /**
     * Count number of specified char occurrences in the specified string.
     */
    public static int countCharOccurrences(String source, char target) {
        int counter = 0;

        //
        // Loop through the string and increment the counter if the
        // target character found in the string. 
        //
        for (int i = 0; i < source.length(); i++) {
            if (source.charAt(i) == target) {
                counter++;
            }
        }
        return counter;
    }
}