CODEWITHSUNDEEP
javastringcountindexof
Michael Fogarty
Michael Fogarty

Reputation: 301

Java String count letter occurrences

I'm a new java programmer. I'm trying to do a search from a user inputed string to find how many occurrences of a particular character there are.

It doesn't quite do what I want it to do as it seems to be displaying the number of characters from the point of the first occurrence of the character. For this project I need to use .indexOf() This is my code.

import java.util.Scanner;
public class SearchingStrings {

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    System.out.println("Please enter the string to test > ");
    String stringToTest = input.nextLine();

    System.out.println("Please enter the letter to count >");

    String letterToCount = input.nextLine();

    // first position found
    int positionOfLetter = stringToTest.indexOf(letterToCount);;

    if (positionOfLetter != -1) {

        int countNumberOfLetters = 1;

        for (int i = positionOfLetter + 1; i < stringToTest.length() - 1; i++) {

            positionOfLetter = stringToTest.substring(positionOfLetter, stringToTest.length()).indexOf(letterToCount);

            if (positionOfLetter != -1) {
                countNumberOfLetters++;
            }
        }

        System.out.println("Number of letters found: " + countNumberOfLetters);

    } else {
        System.out.println("Your letter " + letterToCount + " was not found in the string!");
    }
}
}

Upvotes: 2

Views: 5398

Answers (7)

Hemmels
Hemmels

Reputation: 892

I always liked using split.

longString.split(subStringToCount).length - 1

So in the case of

String longString = "test string with spaces";
String subStringToCount = " ";

return longString.split(subStringToCount).length - 1;

You'll get 3.

Upvotes: 0

Стас Ленивец
Стас Ленивец

Reputation: 1

You can simply do this trick:

int count = stringToTest.replaceAll(letterToCount, "##").length() - stringToTest.length();

Upvotes: 0

Andy Turner
Andy Turner

Reputation: 140328

A cheeky way to count the number of occurrences is to remove all of the occurrences, and compare the length of the resulting string to the original:

String removed = stringToTest.replace(letterToCount, "");
int numOccurrences =
    (stringToTest.length() - removed.length()) / letterToCount.length();

Upvotes: 1

Manos Nikolaidis
Manos Nikolaidis

Reputation: 22224

Using substring to create a new String to search into is quite confusing here apart from inefficient. indexOf has a version that accepts an index to start searching from. That's more efficient as it doesn't make copies of part of the string and simplifies your code quite a lot. E.g.

int positionOfLetter = stringToTest.indexOf(letterToCount);
int countNumberOfLetters = 0;

while (positionOfLetter != -1) {
    countNumberOfLetters++;
    positionOfLetter = stringToTest.indexOf(letterToCount, positionOfLetter + 1);
}

System.out.println("Number of letters found: " + countNumberOfLetters);

The second parameter of indexOf is the start index. Note the +1 otherwise it will find the same char again and never break out of the loop.

Upvotes: 3

Frreshia
Frreshia

Reputation: 11

Seems like a homework question since you wrote you need to use indexOf but you don't. If your purpose is to count a specific letter you can do the following.

int counter=0;
    for(int i=0; i<stringToTest.length();i++){
        if(stringToTest.charAt(i).equals(letterToCount)){
            System.out.println(letterToCount+" appears in "+ i +");
            counter++;
        }
    }
    System.out.println(letterToCount+" appeared "+counter+" times");

This code simply moves through each character of the stringToTest and checks if it is equal to the letter you want. indexOf() is unnecessary

Upvotes: 0

Malte Hartwig
Malte Hartwig

Reputation: 4555

Matcher m = Pattern.compile(letterToCount).matcher(input);
int count = 0;
while (m.find()) {
    count++;
}

should also do the trick.

Upvotes: 1

Darshan Mehta
Darshan Mehta

Reputation: 30819

You are almost there, instead of for loop, you can use do..while loop to achieve this, e.g.:

String s = "test test1 test2";
String letter = "t";
int index = -1, count = 0;
do{
    index = s.indexOf(letter);
    if(index != -1){
        count++;
        s = s.substring(index + 1);
    }
}while(index != -1);

System.out.println(count);

Upvotes: 3

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