C# To Java - C# Programming Exercise

// Importing necessary namespaces
using System; // Importing the System namespace for basic C# functionality
using System.IO; // Importing the IO namespace for file operations
using System.Text.RegularExpressions; // Importing the Regex class for regular expressions

public class CSharpToJavaTranslator
{
    // Method to translate C# code to Java code
    public static void TranslateCSharpToJava(string inputFile, string outputFile)
    {
        // Open the input C# file for reading
        using (StreamReader reader = new StreamReader(inputFile)) // Open the input file in read mode
        {
            // Open the output Java file for writing
            using (StreamWriter writer = new StreamWriter(outputFile)) // Open the output file in write mode
            {
                string line; // Declare a string to store each line from the C# file
                // Read each line from the C# file until the end
                while ((line = reader.ReadLine()) != null)
                {
                    // Translate C# specific syntax to Java equivalents
                    line = TranslateMainMethod(line); // Translate the Main method
                    line = TranslateDataTypes(line); // Translate data types
                    line = TranslateConsoleWriteLine(line); // Translate Console.WriteLine to System.out.println
                    line = TranslateClassDeclaration(line); // Translate class declaration with inheritance
                    line = TranslateReadLineToTryCatch(line); // Translate Console.ReadLine to a try-catch block in Java
                    
                    // Write the translated line to the Java file
                    writer.WriteLine(line); // Write the translated line into the Java file
                }
            }
        }
    }

    // Translate "Main()" to "main(String[] args)"
    private static string TranslateMainMethod(string line)
    {
        // Use a regular expression to replace Main() with main(String[] args)
        return Regex.Replace(line, @"Main\(\)", "main(String[] args)"); 
    }

    // Translate C# data types to Java data types
    private static string TranslateDataTypes(string line)
    {
        // Replace "string" with "String" and "bool" with "boolean" to match Java's types
        line = line.Replace("string", "String"); // Replace string type
        line = line.Replace("bool", "boolean"); // Replace bool type
        return line; // Return the modified line
    }

    // Translate "Console.WriteLine" to "System.out.println"
    private static string TranslateConsoleWriteLine(string line)
    {
        // Replace Console.WriteLine with System.out.println
        return line.Replace("Console.WriteLine", "System.out.println"); 
    }

    // Translate ": " to " extends " if it's part of the class declaration
    private static string TranslateClassDeclaration(string line)
    {
        // If the line contains "class" and ":", change ": " to " extends "
        if (line.Contains("class") && line.Contains(":")) // Check if it's a class declaration with inheritance
        {
            line = line.Replace(":", "extends"); // Replace : with extends for Java inheritance syntax
        }
        return line; // Return the modified line
    }

    // Translate "Console.ReadLine()" to a try-catch block in Java
    private static string TranslateReadLineToTryCatch(string line)
    {
        // If the line contains Console.ReadLine, replace it with a try-catch block for Java input
        if (line.Contains("Console.ReadLine()")) // Check if Console.ReadLine() is in the line
        {
            line = "try {\n" + // Start of try block
                   "    String input = System.console().readLine();\n" + // Read input from console
                   "} catch (Exception e) {\n" + // Catch any exception that occurs
                   "    System.out.println(\"Error reading input\");\n" + // Display an error message if input fails
                   "}"; // End of try-catch block
        }
        return line; // Return the modified line
    }
}

class Program
{
    // Main method where the program execution starts
    static void Main(string[] args)
    {
        // Checking if the user provided the file names
        if (args.Length < 1) // Check if there is at least one argument
        {
            Console.WriteLine("Please provide the input C# file."); // Prompt user to provide the input file
            return; // Exit the program if no file is provided
        }

        string inputFile = args[0]; // Assign the input file name from the command line argument
        string outputFile = Path.ChangeExtension(inputFile, ".java"); // Generate the output file name by changing the extension to .java

        // Checking if the input file exists
        if (!File.Exists(inputFile)) // Check if the input file exists
        {
            Console.WriteLine($"The file {inputFile} does not exist."); // Print error if file does not exist
            return; // Exit the program if the file does not exist
        }

        // Calling the translation method
        CSharpToJavaTranslator.TranslateCSharpToJava(inputFile, outputFile); // Call the method to translate the C# file to Java

        Console.WriteLine($"C# file '{inputFile}' has been successfully translated to Java and saved as '{outputFile}'."); // Notify the user that the translation is complete
    }
}