Find duplicate characters in a String and count the number of occurances using Java

Question

How can I find the number of occurrences of a character in a string?

For example: The quick brown fox jumped over the lazy dog.

Some example

Answer 1

public class CountH {

    public static void main(String[] args) {
        String input = "Hi how are you";

        char charCount = 'h';
        int count = 0;

        input = input.toLowerCase();

        for (int i = 0; i < input.length(); i++) {

            if (input.charAt(i) == charCount) {
                count++;
            }

        }

        System.out.println(count);
    }
}

Answer 2

You could use the following, provided String s is the string you want to process.

Map<Character,Integer> map = new HashMap<Character,Integer>();
for (int i = 0; i < s.length(); i++) {
  char c = s.charAt(i);
  if (map.containsKey(c)) {
    int cnt = map.get(c);
    map.put(c, ++cnt);
  } else {
    map.put(c, 1);
  }
}

Note, it will count all of the chars, not only letters.

Answer 3

A better way would be to create a Map to store your count. That would be a Map<Character, Integer>

You need iterate over each character of your string, and check whether its an alphabet. You can use Character#isAlphabetic method for that. If it is an alphabet, increase its count in the Map. If the character is not already in the Map then add it with a count of 1.

NOTE: - Character.isAlphabetic method is new in Java 7. If you are using an older version, you should use Character#isLetter

    String str = "asdfasdfafk asd234asda";
    Map<Character, Integer> charMap = new HashMap<Character, Integer>();
    char[] arr = str.toCharArray();

    for (char value: arr) {

       if (Character.isAlphabetic(value)) {
           if (charMap.containsKey(value)) {
               charMap.put(value, charMap.get(value) + 1);

           } else {
               charMap.put(value, 1);
           }
       }
    }

    System.out.println(charMap);

OUTPUT: -

{f=3, d=4, s=4, a=6, k=1}

Answer 4

public static void findDuplicate(String letter)
{

    for(int i=0; i<letter.length();i++)
    {
        for( int j=i+1; j<letter.length();j++)
        {
            if(letter.charAt(i)==letter.charAt(j))
            {
                System.out.println(letter.charAt(j));
                break;
            }
        }
    }
}

findDuplicate("JAVA");

The OUTPUT is : A

Answer 5

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        String reverse1;
        String reverse2;
        int count = 0;
        while(n > 0)
        {
            String A = sc.next();
            String B = sc.next();
            reverse1 = new StringBuffer(A).reverse().toString();
            reverse2 = new StringBuffer(B).reverse().toString();
            if(!A.equals(reverse1))
            {
                for(int i = 0; i < A.length(); i++)
                {
                    for(int j = 0; j < A.length(); j++)
                    {
                        if(A.charAt(j) == A.charAt(i))
                        {
                            count++;
                        }
                    }
                    if(count % 2 != 0)
                    {
                        A.replace(A.charAt(i),"");
                        count = 0;
                    }
                }
                System.out.println(A);
            }
            n--;
        } 
    }
}

Answer 6

public class list {

    public static String name(Character k){
        String s="the quick brown fox jumped over the lazy dog.";
        int count=0;
        String l1="";
        String l="";
        List<Character> list=new ArrayList<Character>();
        for(int i1=0;i1<s.length();i1++){
            list.add(s.charAt(i1));
        }
        list.sort(null);
        for (Character character : list) {
            l+=character;
        }
        for (int i1=0;i1<l.length();i1++) {
            if((l.charAt(i1)==k)){
                count+=1;
                l1=l.charAt(i1)+" "+Integer.toString(count);
                if(k==' '){
                    l1="Space"+" "+Integer.toString(count);
                }
            }else{
                count=0;
            }
        }
        return l1;
    }
    public static void main(String[] args){
        String g = name('.');
        System.out.println(g);
    }
}