Occurrence of character in given string

 

Write  Java program that generates the occurrence of each character in a given string:

1 )  package details;

import java.util.HashMap;

public class occurenceOfCharacters {

public static void main(String[] args) {

String s = "hello";

char[] chars = s.toCharArray();

HashMap<Character, Integer> mapData = new HashMap<>();

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

if(mapData.containsKey(s.charAt(i))) {

mapData.put(chars[i], mapData.get(chars[i])+1);

}

else {

mapData.put(chars[i], 1);

}

}

mapData.forEach((k, v) -> System.out.println( k + " " + v));

}

}

Output : e 1

h 1

l 2

o 1

Explanation:

• The program uses a HashMap to store the characters as keys and their respective counts as values.
• It loops through each character in the string and updates the map accordingly.
• Finally, it prints out the occurrences of each character.

2 )  import java.util.HashMap;

import java.util.Map;

public class CharacterOccurrence {

    public static void main(String[] args) {

        String inputString = "programming";  // You can change the string here

        countCharacterOccurrences(inputString);

    }

    public static void countCharacterOccurrences(String str) {

        // Creating a map to store the frequency of each character

        Map<Character, Integer> charCountMap = new HashMap<>();

        // Loop through each character of the string

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

            char c = str.charAt(i);

            // Directly use getOrDefault to handle count updates

            charCountMap.put(c, charCountMap.getOrDefault(c, 0) + 1);

        }

        // Display the result

        System.out.println("Character occurrences in the string:");

        for (Map.Entry<Character, Integer> entry : charCountMap.entrySet()) {

            System.out.println(entry.getKey() + ": " + entry.getValue());

        }

    }

}

Key Improvements:

• getOrDefault(c, 0): This allows us to retrieve the current count for a character or return 0 if it doesn't exist. We then increment this value directly, eliminating the need for an if-else check.
• Single pass through the string: We're directly iterating over the string's characters using charAt(i), which avoids converting the string to a character array, making it more memory efficient.

Output :

Character occurrences in the string:

p: 1

a: 3

r: 2

v: 1

g: 2

i: 1

j: 1

m: 2

n: 1

o: 1

3) public static void countCharacterOccurrences(String str) {

        // Using Java Streams to count character occurrences

        Map<Character, Long> charCountMap = str.chars()

                                               .mapToObj(c -> (char) c)

                                               .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

        // Display the result

        charCountMap.forEach((key, value) -> System.out.println(key + ": " + value));

    }

Explanation:

• str.chars() converts the string into an IntStream of character values.
• .mapToObj(c -> (char) c) converts the primitive int values back to Character objects.
• Collectors.groupingBy(Function.identity(), Collectors.counting()) groups characters and counts their occurrences

Ouptut:

p: 1

a: 3

r: 2

v: 1

g: 2

i: 1

j: 1

m: 2

n: 1

o: 1