Scala Programming: Exchange the first and last characters in a given string and return the new string

Last update on February 05 2025 12:54:24 (UTC/GMT +8 hours)

Write a Scala program to exchange the first and last characters in a given string and return the new string.

Pre-Knowledge (Before You Start!)

Before attempting this exercise, you should be familiar with the following concepts:

Scala Objects: Understanding how to define objects using the object keyword.
Functions in Scala: How to create functions with parameters and return values.
String Operations: Using methods like charAt() and substring() to manipulate strings.
String Length: Using the length property to determine the number of characters in a string.
Conditional Statements: Implementing if-else conditions to check for special cases (e.g., strings with only one character).
String Concatenation: Combining substrings using the + operator.
Main Method: Understanding the structure of the main() function in Scala.
Printing to Console: Using println() to display results.

Hints (Try Before Looking at the Solution!)

Try to solve the problem using these hints:

Hint 1: Define an object in Scala to contain the function.
Hint 2: Create a function that accepts a string as an argument.
Hint 3: Find the length of the string using length.
Hint 4: If the string has only one character, return it as is.
Hint 5: Extract the first and last characters using charAt().
Hint 6: Extract the middle part of the string using substring().
Hint 7: Concatenate the last character, the middle part, and the first character to form the new string.
Hint 8: Test your function with different string inputs, including edge cases like single-character strings.

Sample Solution:

Scala Code:

// Define an object named scala_basic
object scala_basic {
  // Define a function named test with parameter str1 of type String, returning a String
  def test(str1: String): String = 
    {
      // Calculate the length of the input string and assign it to the variable len
      val len = str1.length
      
      // Check if the length is less than or equal to 1; if true, return the string as is
      if (len <= 1) 
        str1
      else 
        // If false, rearrange the string by moving the last character to the front and vice versa
        str1.charAt(len - 1) + str1.substring(1, len - 1) + str1.charAt(0)
    }   

   // Define the main method, which is the entry point of the program
   def main(args: Array[String]): Unit = {
      // Print the result of calling test with the argument "Scala"
      println("Result: " + test("Scala"))
      
      // Print the result of calling test with the argument "abcd"
      println("Result: " + test("abcd"))
      
      // Print the result of calling test with the argument "ab"
      println("Result: " + test("ab"))
      
      // Print the result of calling test with the argument "a"
      println("Result: " + test("a"))
    }
}

Sample Output:

Result: acalS
Result: dbca
Result: ba
Result: a

Explanation:

Here is the break down of the said Scala code:

object scala_basic {: This declares an object named scala_basic.
def test(str1: String): String =: This line defines a function named test that takes a parameter str1 of type String and returns a String. The function rearranges the input string by moving the last character to the front and the first character to the end.
val len = str1.length: This line calculates the length of the input string str1 and assigns it to the variable len.
if (len <= 1) str1 else str1.charAt(len - 1) + str1.substring(1, len - 1) + str1.charAt(0): This is a conditional expression inside the "test()" function. If the length of the string is less than or equal to 1, it returns the string as is. Otherwise, it rearranges the string by concatenating the last character, the substring from index 1 to len - 1, and the first character.
def main(args: Array[String]): Unit = {: This line defines the main method, which is the entry point of the program. It takes an array of strings (args) as its parameter and returns Unit (similar to void in other languages).
println("Result: " + test("Scala")): This line calls the "test()" function with the argument "Scala", concatenates the result with the string "Result: ", and prints the entire string to the console.
println("Result: " + test("abcd")): Similar to the previous line, this calls the "test()" function with the argument "abcd".
println("Result: " + test("ab")): Another call to the "test()" function with the argument "ab".
println("Result: " + test("a")): Another call to the "test()" function with the argument "a".

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