count frequency of characters in string using java 

In most of the interviews , we always get this question from interviewer :

program to count frequency of characters in string ?

program to count number of times character occurred in given String?

program to count number of times character repeated in statement ?

today we are going to see the solution for this , using java we will print count of frequency of characters in string :

import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;

public class CountFrequency {
 public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		String input = null;
		int option=0;
		try {
			do {
				System.out.println("Enter 1 to test new String:  ");
				System.out.print("\nEnter 2 for exit : ");
				try {
				option = scn.nextInt();
				}
				catch(Exception e) {
					System.out.println("Wrong input ,Please Enter 1 or 2 ");
					e.printStackTrace();
					option=2;
				}
				
				if (option == 1) {
					System.out.println("Enter String here ->");
					input = scn.next();
					countNumberOfCharacters(input);
				}
				
				else if(option==2) {
					System.out.println("Program is stopped, run again to test");
				}
				else {
					System.out.println("Enter either 1 or 2");
				}
			} while (option != 2);
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			scn.close();
		}
	}

	private static void countNumberOfCharacters(String input) {
		char[] myArray = input.toCharArray();
		Map<Character, Integer> myMap = new HashMap<Character, Integer>();
		for (int i = 0; i < myArray.length; i++) {
			int frequency = 0;
			char tempKey = myArray[i];
			if (!myMap.containsKey(tempKey)) {
				myMap.put(tempKey, frequency + 1);
			} else {
				myMap.put(tempKey, myMap.get(tempKey) + 1);
			}
		}
		System.out.println("Count is as below :");
		for (Entry<Character, Integer> myEntry : myMap.entrySet()) {
			System.out.println( myEntry.getKey() + ": " + myEntry.getValue());
		}
	}

}

Output :

Enter 1 to test new String:  

Enter 2 for exit : 1
Enter String here ->
crtr4u.com
Count is as below :
r: 2
c: 2
t: 1
4: 1
u: 1
m: 1
.: 1
o: 1
Enter 1 to test new String:  

Enter 2 for exit : 1
Enter String here ->
aaBBcccd
Count is as below :
a: 2
B: 2
c: 3
d: 1
Enter 1 to test new String:  

Enter 2 for exit : 2
Program is stopped, run again to test

Happy Learning, Keep Coding.