Given a string and a character, the task is to create a function that uses the Stream API to detect occurrences of certain characters in the string.

Examples:

Input: str = "geeksforgeeks", c = 'e'
Output: 4
'e' appears four times in str.

Input: str = "abccdefgaa", c = 'a' 
Output: 3
'a' appears three times in str.

Approach:

• Converting a string to a character stream
• Use the filter() function to ensure that the characters in the stream are the characters to be counted.
• Count matching characters with count() function

Below is the implementation of the above approach:

// Java program to count occurrences
// of a character using Stream

import java.util.stream.*;

class GFG {

	// Method that returns the count of the given
	// character in the string
	public static long count(String s, char ch)
	{

		return s.chars()
			.filter(c -> c == ch)
			.count();
	}

	// Driver method
	public static void main(String args[])
	{
		String str = "geeksforgeeks";
		char c = 'e';
		System.out.println(count(str, c));
	}
}

Output:

4