Index of first repeated character in a string.

Let me break down and elaborate on the Java code snippet you've provided. This code is designed to find the first repeated character in a string and then print its index.

Code Explanation

1. String Initialization

java
String repeadted = "adffda";

• A string repeadted is initialized with the value "adffda". The word seems like a typo, and it probably meant "repeated."

2. Creating a Set to Track Characters

java
Set<Character> set1 = new HashSet<>();

• A HashSet named set1 is created to store characters from the string repeadted.
• The HashSet data structure is chosen because it does not allow duplicate elements, making it perfect for detecting repeated characters.

3. Finding the First Repeated Character

java
char ch1 = (char) repeadted.chars()
                            .filter(c -> !set1.add((char) c))
                            .findFirst()
                            .getAsInt();

• repeadted.chars(): This method converts the string repeadted into an IntStream of its character codes. Each character in the string is represented by its corresponding ASCII value.
• filter(c -> !set1.add((char) c)):
  • The filter method is used to process each character's ASCII value.
  • (char) c: Casts the integer ASCII value c back to a char.
  • !set1.add((char) c): Attempts to add the character to set1.
    • The add method returns true if the character is not already in the set and successfully adds it.
    • If the character is already in the set (indicating it’s a duplicate), add returns false.
  • The filter method only retains those characters that return false from set1.add((char) c)—i.e., the characters that are duplicates.
• findFirst(): Returns an OptionalInt describing the first element of this stream (the first duplicated character found).
• getAsInt(): Retrieves the integer value of the OptionalInt, which is the ASCII code of the first repeated character.
• (char) ...: Casts the integer ASCII code back to a char, assigning it to ch1.

4. Printing the Index of the First Repeated Character

java
System.out.println(repeadted.indexOf((char) ch1));

• repeadted.indexOf((char) ch1): Finds the index of the first occurrence of the character ch1 in the string repeadted.
• System.out.println(...): Prints the index to the console.

What Does This Program Do?

1. Initialization: The program initializes a string, "adffda".
2. Finding the First Repeated Character:
   • It uses a HashSet to keep track of characters it has seen.
   • As it iterates through each character in the string (using chars()), it tries to add each character to the set.
   • If adding a character fails (because the character is already in the set), that character is identified as the first repeated character.
3. Finding and Printing the Index:
   • The program then finds the index of this first repeated character in the original string using indexOf and prints it.

Example Walkthrough

For the string "adffda":

1. Characters processed:
   • 'a' → added to set.
   • 'd' → added to set.
   • 'f' → added to set.
   • 'f' → not added (already in set). First repeated character.
2. Find index:
   • repeadted.indexOf('f') → 2 (zero-based index).

Output:

2

The output 2 is printed, which is the index of the first occurrence of the repeated character 'f' in the string "adffda".

Summary

This code snippet efficiently finds the first repeated character in a string and prints its index using Java 8 features like streams, HashSet, and lambda expressions.

 String repeadted="adffda";

Set set1=new HashSet<>();

	char ch1=(char) repeadted.chars()

                                           .filter(c->!set1.add((char)c))

                                            .findFirst()

                                             .getAsInt();

	

System.out.println(repeadted.indexOf((char)ch1));