How do I count the number of occurrences of a char in a String?

Question

I have the string a.b.c.d. I want to count the occurrences of '.' in an idiomatic way, preferably a one-liner. (Previously I had expressed this constraint as "without a loop", in case you're wondering why everyone's trying to answer without using a loop).

Answer 1

There are no String methods, or any other core-java methods for that matter, that provides an occurrence count - and therefore, a one line solution.

However, Java 8 offers 'Lambda Function' magic - and therefore the following code fragment works.

This displayed: " '.' Count: 6 "

public static void main(String[] args) {

String myString = "a.b.c.d.e.f.g";

long count = myString.chars().filter(charCount -> charCount == '.').count(); /// <<<<<<<

System.out.printf("'.' Count: %d\n", count);

}

It's difficult to explain without getting into Lambda Expressions - but let's just say that the 3rd line above is assigned a filter count - and we're filtering by characters that equal "."

I could change the code above to the following and get a count of 12.

You see why, right?

public static void main(String[] args) {

String myString = "a.b.c.d.e.f.g";

long count = myString.chars().filter(charCount -> charCount != 'f').count();

System.out.printf("'.' Count: %d\n", count);

}

Otherwise, you can of course do this the brute force way using a loop - or recursion.

Good luck.

--Lou