// Need this import for reading data:
import java.io.*;

// counting the number of occurrences of 'a'
// in the input string
public class CharCounting {

    public static void main (String [] args) throws IOException {
	// Create a buffered reader
	BufferedReader in = new BufferedReader(
			new InputStreamReader(System.in));
	// string for storing a line of input
	String line;

	// prompt the user:
	System.out.print("Please say something: ");
	// read the line:
	line = in.readLine();
	
	// set up the counter:
	int counter = 0;
	// store the length of the string:
	int len = line.length();

	// go through each character, count 'a':
	for (int i = 0; i < len; ++i) {
	    if (line.charAt(i) == 'a') 
		counter++;
	}
	System.out.println("The string has " + counter + " letters a");
    }

}

This is an example from CSci 1211 course.

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