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

Using Eclipse Collections CharAdapter and CharBag:

CharBag bag = 
    Strings.asChars("The quick brown fox jumped over the lazy dog.").toBag();

Assert.assertEquals(1, bag.occurrencesOf('a'));
Assert.assertEquals(4, bag.occurrencesOf('o'));
Assert.assertEquals(8, bag.occurrencesOf(' '));
Assert.assertEquals(1, bag.occurrencesOf('.'));

Note: I am a committer for Eclipse Collections

Answer 2

In java... using for loop:

import java.util.Scanner;

/**
 *
 * @author MD SADDAM HUSSAIN */
public class Learn {

    public static void main(String args[]) {

        Scanner sc = new Scanner(System.in);
        String input = sc.next();
        char process[] = input.toCharArray();
        boolean status = false;
        int index = 0;
        for (int i = 0; i < process.length; i++) {
            for (int j = 0; j < process.length; j++) {

                if (i == j) {
                    continue;
                } else {
                    if (process[i] == process[j]) {
                        status = true;
                        index = i;
                        break;
                    } else {
                        status = false;

                    }
                }

            }
            if (status) {
                System.out.print("" + process[index]);

            }
        }
    }
}

Answer 3

 void Findrepeter(){
    String s="mmababctamantlslmag";
    int distinct = 0 ;

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

        for (int j = 0; j < s.length(); j++) {

            if(s.charAt(i)==s.charAt(j))
            {
                distinct++;

            }
        }   
        System.out.println(s.charAt(i)+"--"+distinct);
        String d=String.valueOf(s.charAt(i)).trim();
        s=s.replaceAll(d,"");
        distinct = 0;

    }

}

Answer 4

public class DuplicateValue {

    public static void main(String[] args) {

        String s = "hezzz";

        char []st=s.toCharArray();

        int count=0;

        Set<Character> ch=new HashSet<>();
        for(Character cg:st){
            if(ch.add(cg)==false){
                int occurrences = Collections.frequency(ch, cg);
                count+=occurrences;
                if(count>1){
                System.out.println(cg + ": This character exist more than one time");
                }
                else{
                System.out.println(cg);
                }
            }
        }

        System.out.println(count);
    }
}

Answer 5

This is the implementation without using any Collection and with complexity order of n. Although the accepted solution is good enough and does not use Collection as well but it seems, it is not taking care of special characters.

import java.util.Arrays;

public class DuplicateCharactersInString {
    public static void main(String[] args) {
        String string = "check duplicate charcters in string";
        string = string.toLowerCase();
        char[] charAr = string.toCharArray();
        Arrays.sort(charAr);
        for (int i = 1; i < charAr.length;) {
            int count = recursiveMethod(charAr, i, 1);
            if (count > 1) {
                System.out.println("'" + charAr[i] + "' comes " + count + " times");
                i = i + count;
            } else
                i++;
        }
    }

    public static int recursiveMethod(char[] charAr, int i, int count) {
        if (ifEquals(charAr[i - 1], charAr[i])) {
            count = count + recursiveMethod(charAr, ++i, count);
        }
        return count;
    }

    public static boolean ifEquals(char a, char b) {
        return a == b;
    }
}

Output :

' ' comes 4 times
'a' comes 2 times
'c' comes 5 times
'e' comes 3 times
'h' comes 2 times
'i' comes 3 times
'n' comes 2 times
'r' comes 3 times
's' comes 2 times
't' comes 3 times

Answer 6

Finding the duplicates in a String:

Example 1 : Using HashMap

public class a36 {
    public static void main(String[] args) {
        String a = "Gini Rani";
        fix(a);
    }//main
    public static void fix(String a ){
        Map<Character ,Integer> map = new HashMap<>();
        for (int i = 0; i <a.length() ; i++ ) {
        char ch = a.charAt(i);
                map.put(ch , map.getOrDefault(ch,0) +1 );
        }//for

       List<Character> list = new ArrayList<>();
       Set<Map.Entry<Character ,Integer> > entrySet = map.entrySet();

       for (  Map.Entry<Character ,Integer> entry : entrySet) {
             list.add( entry.getKey()  ); 

             System.out.printf(  " %s : %d %n" ,  entry.getKey(), entry.getValue()           );
       }//for
       System.out.println("Duplicate elements => " + list);

    }//fix
}

Example 2 : using Arrays.stream() in Java 8

public class a37 {
    public static void main(String[] args) {
        String aa = "Protijayi Gini";
        String[] stringarray = aa.split("");

    Map<String , Long> map =  Arrays.stream(stringarray)
        .collect(Collectors.groupingBy(c -> c , Collectors.counting()));
        map.forEach( (k, v) -> System.out.println(k + " : "+ v)        );
    }
}