Frequently Asked Java Program 08: Program to find occurrence of individual characters in a given string.

Hello Folks,

As part of Frequently Asked Java Programs In Interviews For Freshers And Experienced, in this post we will learn to develop a java program to find out occurrence of individual characters in a given string.

Logic:

1. To get input from user, we will use Scanner class.
2. We will use Map interface concept here which deals in key-value pair.
3. We will convert given string in to a char array.
4. We will iterate char array index by index and will add in to Map if char does not exist already. If it exists we will increase value by one.

Java Program:-

package MakeSeleniumEasy;

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
 
public class CountOfCharsInString {
 
    /**
     * @param inputString
     * @return Map
     * This method will save all char in a Map.
     */
    public Map getCountOfChar(String inputString)
    {     
        Map charDictionary = new HashMap();
        // converting given string in to lower case
        String inoutCharInLowerCase=inputString.toLowerCase();
        // Converting string in to char array
        char[] chrsInString = inoutCharInLowerCase.toCharArray();
        // iterating char array 
        /*
         * Map stores as key and value pairs where key should be unique. 
         * We will consider character as a key. If key does not exists, we will add
         * in to key with value 1. If key exists, we will just increment the value by one.
         */
        for(Character ch:chrsInString){
            if(charDictionary.containsKey(ch)){
            	charDictionary.put(ch, charDictionary.get(ch)+1);
            } else {
            	charDictionary.put(ch, 1);
            }
        }
        return charDictionary;
        
    }
    
    /**
     * @param charCountMap
     * This method will print all characters with number of occurrence in a string.
     * If char is white space, it will be shown as "White space".
     */
    public void printCharWithCount(Map charCountMap)
    {
    	Set keys = charCountMap.keySet();
        for(Character ch:keys)
        {
        	if(ch==' ')
        	{
        		System.out.println("White space" +" = "+charCountMap.get(ch));
        	}
        	else
        	{
        		System.out.println(ch +" = "+charCountMap.get(ch));
        	}
        }
    }
    
    /**
     * @param charCountMap
     * This method can be used to print duplicate characters in a given string. 
     */
    public void printDuplicateCharsWithOccurance(Map charCountMap)
    {
    	System.out.println("Duplicate characters are:");
    	Set keys = charCountMap.keySet();
        for(Character ch:keys)
        {
        	if(!(ch==' '))
        	{
	        	if(charCountMap.get(ch) > 1)
	            {
	                System.out.println(ch);
	            }
        	}
        }
        
    }
     
    public static void main(String a[])
    {
    	Scanner sc= new Scanner(System.in);
    	System.out.println("Please provide a string to get count of characters: ");
    	String inputString= sc.nextLine();
    	CountOfCharsInString object = new CountOfCharsInString();
    	Map map= object.getCountOfChar(inputString);
    	object.printCharWithCount(map);
    	object.printDuplicateCharsWithOccurance(map);
    }
}

Output:

Please provide a string to get count of characters:
Amod Mahajan
White space = 1
a = 4
d = 1
h = 1
j = 1
m = 2
n = 1
o = 1
Duplicate characters are:
a
m

======================================================================

Please provide a string to get count of characters:
Make Selenium Easy
White space = 2
a = 2
s = 2
e = 4
u = 1
i = 1
y = 1
k = 1
l = 1
m = 2
n = 1
Duplicate characters are:
a
s
e
m

If you have nay doubt or suggestions feel free to comment.
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