Counting no of Occurrence of a particular character inside a string in Java

Question

I have a string.

a.b.c.d

I want to count the occurrences of '.' in an idiomatic way, preferably a one-liner.

Answer 1

This is a summarized answer for all the forms of solution to the problem in a one-liner:

   String testString = "a.b.c.d";

1) Using Apache Commons

int apache = StringUtils.countMatches(testString, ".");
System.out.println("apache = " + apache);

2) Using Spring Framework's

int spring = org.springframework.util.StringUtils.countOccurrencesOf(testString, ".");
System.out.println("spring = " + spring);

3) Using replace

int replace = testString.length() - testString.replace(".", "").length();
System.out.println("replace = " + replace);

4) Using replaceAll (case 1)

int replaceAll = testString.replaceAll("[^.]", "").length();
System.out.println("replaceAll = " + replaceAll);

5) Using replaceAll (case 2)

int replaceAllCase2 = testString.length() - testString.replaceAll("\\.", "").length();
System.out.println("replaceAll (second case) = " + replaceAllCase2);

6) Using split

int split = testString.split("\\.",-1).length-1;
System.out.println("split = " + split);

7) Using Java8 (case 1)

long java8 = testString.chars().filter(ch -> ch =='.').count();
System.out.println("java8 = " + java8);

8) Using Java8 (case 2), may be better for unicode than case 1

long java8Case2 = testString.codePoints().filter(ch -> ch =='.').count();
System.out.println("java8 (second case) = " + java8Case2);

9) Using StringTokenizer

int stringTokenizer = new StringTokenizer(" " +testString + " ", ".").countTokens()-1;
System.out.println("stringTokenizer = " + stringTokenizer);

Note: Be carefull for the StringTokenizer, for a.b.c.d it will work but for a...b.c....d or ...a.b.c.d or a....b......c.....d... or etc. it will not work. It just will count for . between characters just once

Just a suggestion : 

Sooner or later, something has to loop. It's far simpler for you to write the (very simple) loop than to use something like split which is much more powerful than you need.

By all means encapsulate the loop in a separate method, e.g.

public static int countOccurrences(String haystack, char needle)
{
    int count = 0;
    for (int i=0; i < haystack.length(); i++)
    {
        if (haystack.charAt(i) == needle)
        {
             count++;
        }
    }
    return count;
}

Hope it helps...!!!

Answer 2

We can find out the no. of occurence of a particular character in String using:

int count = StringUtils.countMatches("a.b.c.d", ".");

For Sparing Framework:

int occurance = StringUtils.countOccurrencesOf("a.b.c.d", ".");