How To Count Occurrences Of A Grapheme Inwards String - Coffee Programming Practise Example

Write a computer program to count the discover of occurrences of a graphic symbol inwards String is ane of the mutual programming interview questions non only inwards Java but equally good inwards other programming languages similar C or C++.  As String inwards a real pop topic on programming interviews together with at that spot are lot of skilful programming practise on String similar "count discover of vowels or consonants inwards String", "count discover of characters inwards String" , How to contrary String inwards Java using recursion or without using StringBuffer etc, it becomes extremely of import to induce got company noesis of String in Java or whatever other programming language. Though, this query is by together with large used to examination candidate's coding mightiness i.e. whether he tin convert logic to code or not.

In Interview, nigh of the fourth dimension Interviewer volition inquire you lot to write a computer program without using whatever API method,  as Java is real rich together with it ever only about sort of prissy method to produce the job, But it equally good of import to know rich Java together with opened upward origin libraries for writing production lineament code.

Anyway, inwards this question, nosotros volition encounter both API based together with non-API based(except few) ways to count a discover of occurrences of a graphic symbol inwards String on Java.

Java computer program to count occurrences of a graphic symbol inwards String

static method countOccurrenceOf(String, character) which takes a String together with graphic symbol together with returns occurrence of graphic symbol into that String.

After that, nosotros volition encounter Apache common StringUtils bird for counting occurrence of a graphic symbol inwards String. Apache common StringUtils render countMatches() method which tin live on used to count the occurrence of ane graphic symbol or substring.

Finally, nosotros volition encounter the nigh unproblematic agency of counting graphic symbol using touchstone for loop together with Java five enhanced for loop. This solution tin live on extended non only to finding the occurrence of graphic symbol but equally good finding occurrences of a substring.

Btw, if you lot are solving this query equally constituent of your Java interview preparation, you lot tin equally good cheque Cracking the Coding Interview, a collection of 189 programming questions together with solutions from diverse programming undertaking interviews. Your perfect companion for developing coding feel required solving these kinds of problems on interviews. 

Now, let's encounter the Java computer program to count discover of occurrence of whatever graphic symbol on String:

import org.springframework.util.StringUtils;

/**
 * Java computer program to count the discover of occurrence of whatever graphic symbol on String.
 * @author Javin Paul
 */
public class CountCharacters {

    public static void main(String args[]) {
         
        String input = "Today is Monday"; //count discover of "a" on this String.
     
        //Using Spring framework StringUtils bird for finding occurrence of only about other String
        int count = StringUtils.countOccurrencesOf(input, "a");
     
        System.out.println("count of occurrence of graphic symbol 'a' on String: " +

                " Today is Monday' using Spring StringUtils " + count);

     
        //Using Apache common lang StringUtils class
        int discover = org.apache.commons.lang.StringUtils.countMatches(input, "a");
        System.out.println("count of graphic symbol 'a' on String: 'Today is Monday' using common StringUtils " + number);
     
        //counting occurrence of graphic symbol alongside loop
        int charCount = 0;
        for(int i =0 ; i<input.length(); i++){
            if(input.charAt(i) == 'a'){
                charCount++;
            }
        }
        System.out.println("count of graphic symbol 'a' on String: 'Today is Monday' using for loop  " + charCount);
     
        //a to a greater extent than elegant agency of counting occurrence of graphic symbol inwards String using foreach loop
     
        charCount = 0; //resetting graphic symbol count
        for(char ch: input.toCharArray()){
            if(ch == 'a'){
                charCount++;
            }
        }    
        System.out.println("count of graphic symbol 'a' on String: 'Today is Monday' using for each loop  " + charCount);
    }
 
       
}

Output
count of occurrence of graphic symbol 'a' on String: 'Today is Monday' using Spring StringUtils 2
count of graphic symbol 'a' on String: 'Today is Monday' using common StringUtils 2
count of graphic symbol 'a' on String: 'Today is Monday' using for loop  2
count of graphic symbol 'a' on String: 'Today is Monday' using for each loop  2

Well, the beauty of this questions is that Interviewer tin twist it on many ways, they tin inquire you lot to write a recursive business office to count occurrences of a detail character or they tin fifty-fifty inquire to count how many times each graphic symbol has appeared.

So if a String contains multiple characters together with you lot demand to shop count of each character, regard using HashMap for storing graphic symbol equally primal together with discover of occurrence equally value. Though at that spot are other ways of doing it equally good but I similar the HashMap agency of counting graphic symbol for simplicity.

Further Learning
The Coding Interview Bootcamp: Algorithms + Data Structures
Data Structures together with Algorithms: Deep Dive Using Java
Write a computer program to uncovering factorial of discover using recursion

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How to cheque if a discover is Armstrong discover inwards Java

How to cheque prime numbers inwards Java

How to contrary discover inwards Java without using API method