✨ Let’s walk through the logic like a pro storyteller!
🎯 Objective of the Program
We are writing a Java program to:
Detect characters in a string that appear more than once.
Print those duplicate characters along with how many times they occur.
🚀 Step-by-Step Explanation of Each Line (Without Code)
1️⃣ Package Declaration
The code is organized into a package named com.basics.strings.testing.
Packages are like folders in Java to group related classes logically.
2️⃣ Import Statement
Java's HashMap and Map classes are imported from the java.util package.
This gives us access to collection tools that let us store key-value pairs.
3️⃣ Class Declaration
A public class is declared with a name (e.g., DuplicateCharacters).
This class will contain all the logic we need.
4️⃣ Main Method
The program starts from the main method.
It’s the entry point for Java execution—everything begins here.
5️⃣ Declare the String
A string variable is defined (e.g., "programming").
This is the input data we want to analyze.
6️⃣ Create a HashMap
A HashMap is created to store each character of the string as a key.
The value for each key will be the number of times the character appears.
Think of it like: {‘p’ : 1, ‘r’ : 2, ‘o’ : 1, ...}
7️⃣ Convert the String to a Character Array
The string is broken into individual characters.
This lets us analyze each character one by one.
8️⃣ Loop Over Each Character
A loop is used to go through each character in the array.
For every character:
If it already exists in the map, we increment its count.
If it doesn’t exist, we add it with an initial count of 1.
This is done using a method that returns the existing count or a default of 0.
9️⃣ Print Header for Output
A simple message like “Duplicate characters:” is printed to label the results.
🔟 Loop Over the Map Entries
Another loop is used to check all key-value pairs in the map.
For each entry:
If the value (frequency) is greater than 1, it means the character is duplicated.
That character and its count are printed as output.
🧠 What Concepts Are Used Here?
Strings: Basic Java objects used to hold text.
Loops: To go through arrays and collections.
HashMap: A powerful Java collection to store and retrieve data by keys.
Conditionals: To check if a character is a duplicate (count > 1).
getOrDefault() Method: A neat shortcut to avoid checking nulls before inserting into the map.
🏁 Final Output Example
If your input is:
"programming"
The program will print:
Duplicate characters:
r -> 2 times
g -> 2 times
m -> 2 times
✅ Conclusion: What Did You Learn?
How to track character occurrences in a string.
How to use a HashMap for frequency counting.
The beauty of combining loops, collections, and conditional logic.
Practical use of getOrDefault() to make cleaner and safer Java code.
Abeginner-friendly foundation for string manipulation tasks in Java.
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