How to Efficiently Count Character Frequencies in Strings with Java?

Character Frequency in Strings: A Comprehensive Guide

Determining the frequency of characters within a text string is a common programming task. This article explores an efficient solution for counting character occurrences using a Map in Java.

To implement this solution, create a HashMap where the keys represent characters and the values represent their respective frequencies. Iterate through each character in the input string and perform the following steps:

1. Check if the current character already exists in the Map.
2. If it exists, increment its frequency count.
3. If it does not exist, add it to the Map with an initial count of 1.

Here's an example code that demonstrates this approach:

<code class="java">Map<Character, Integer> frequencyMap = new HashMap<>();
String input = "aasjjikkk";

for (int i = 0; i < input.length(); i++) {
    char character = input.charAt(i);
    Integer frequency = frequencyMap.get(character);
    if (frequency != null) {
        frequencyMap.put(character, frequency + 1);
    } else {
        frequencyMap.put(character, 1);
    }
}</code>

This code results in a Map where keys represent characters ('a', 's', 'j', 'i', 'k') and values represent their corresponding counts (2, 1, 2, 1, 3). By accessing this Map, you can easily obtain the frequency of each character in the input string.

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