How to Remove Characters at Odd Positions in a String Using Java

When you’re learning Java, one of the common tasks you’ll come across is manipulating strings. In this blog, we’ll walk you through a simple program that removes characters at odd positions from a string. Don’t worry if you’re just starting out—I’ll explain everything step by step!

Understanding the Task

Let’s say you have a string like "Hello World", and you want to remove the characters at odd positions. In programming, string indices usually start at 0, so the characters at “odd positions” are those at index 1, 3, 5, and so on. Our goal is to remove these characters and only keep those at even positions.

For example, from "Hello World", the program should give us "HloWrd".

The Code

Here’s the Java code that accomplishes this task:

import java.util.Scanner;

public class RemoveCharAtOddPosition {

    // Method to remove characters at odd positions in the string
    public static String removeCharAtOddPosition(String str) {
        // Create an empty string to store the result
        StringBuilder sb = new StringBuilder();

        // Loop through each character in the string
        for (int i = 0; i < str.length(); i++) {
            // Check if the position is even (0, 2, 4, ...)
            if (i % 2 == 0) {
                // If the position is even, add the character to the result
                sb.append(str.charAt(i));
            }
        }

        // Return the final string with characters at odd positions removed
        return sb.toString();
    }

    // Main method to run the program
    public static void main(String[] args) {
        // Create a Scanner object to read input from the user
        Scanner scan = new Scanner(System.in);

        // Prompt the user to enter a string
        System.out.println("Enter a string:");
        String str = scan.nextLine();

        // Call the method to remove characters at odd positions
        String newString = removeCharAtOddPosition(str);

        // Print the result
        System.out.println("String after removing characters at odd positions: " + newString);
    }
}

Now, let’s break down what each part of the code does.

Code Breakdown

1. Importing the Scanner Class

import java.util.Scanner;

The Scanner class is used to get user input. In this program, we’ll use it to read the string that the user wants to process.

2. The `removeCharAtOddPosition` Method

public static String removeCharAtOddPosition(String str) {
    StringBuilder sb = new StringBuilder();

    for (int i = 0; i < str.length(); i++) {
        if (i % 2 == 0) {
            sb.append(str.charAt(i));
        }
    }

    return sb.toString();
}

StringBuilder sb = new StringBuilder();: We use StringBuilder to build our result string. It’s more efficient than using string concatenation in a loop.
Looping Through the String: The for loop goes through each character in the string using the index i.
Checking the Index: The if (i % 2 == 0) statement checks if the index i is even. The % operator gives the remainder of dividing i by 2. If the remainder is 0, it means i is even, and we keep that character.
Appending to StringBuilder: If the index is even, we use sb.append(str.charAt(i)); to add the character at that position to our result string.
Returning the Result: Finally, sb.toString() converts the StringBuilder into a string that we can return.

3. The `main` Method

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);

    System.out.println("Enter a string:");
    String str = scan.nextLine();

    String newString = removeCharAtOddPosition(str);

    System.out.println("String after removing characters at odd positions: " + newString);
}

Reading User Input: The program starts by asking the user to enter a string. The scan.nextLine() method reads this input.
Calling the Method: We then call removeCharAtOddPosition(str) to process the string and remove the characters at odd positions.
Displaying the Result: Finally, we print out the modified string.

Running the Program

When you run this program, it will ask you to enter a string. After you input the string, the program will output the new string with characters at odd positions removed.

For example:

Enter a string:
Hello World
String after removing characters at odd positions: HloWrd

Summary

In this blog, we learned how to create a simple Java program that removes characters at odd positions in a string. We used basic concepts like loops, conditionals, and string manipulation to achieve this. This exercise is a great way to practice working with strings and understanding how to manipulate them in Java.

Feel free to experiment with different strings and see how the program behaves!