Filtering and copying emails to a .txt file from all the .txt files in a Directory

using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

using System.Threading.Tasks;

namespace FilesExamples

{

    class EmailFilter

    {

        public static void emas()

        {

            try

            {

                string FolderPath = @"D:\Practice Applications\Supported Files\randomemailtext\filtered\Input path";

                string line;

                var Outputdirectory = new DirectoryInfo(@"D:\Practice Applications\Supported Files\randomemailtext\filtered");

                // Loop to search all the .txt files in the directory path

                foreach (string file in Directory.EnumerateFiles(FolderPath, "*.txt", SearchOption.AllDirectories))

                {

                    StringReader srr = new StringReader(File.ReadAllText(file));

                    string dynamicFile = "OutputSample" + ".txt";

                    var Ofile = new FileInfo(Path.Combine(Outputdirectory.FullName, dynamicFile));

                    using (Stream stream = Ofile.OpenWrite())

                    using (StreamWriter writer = new StreamWriter(stream))

                    {

                        Console.WriteLine("Copying, Please Wait...");

                        while ((line = srr.ReadLine()) != null)

                        {

                            const string MatchEmailPattern =

                            @"(([\w-]+\.)+[\w-]+|([a-zA-Z]{1}|[\w-]{2,}))@"

                            + @"((([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\." + @"([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])\.([0-1]?[0-9]{1,2}|25[0-5]|2[0-4][0-9])){1}|" + @"([a-zA-Z]+[\w-]+\.)+[a-zA-Z]{2,4})";

                            Regex rx = new Regex(MatchEmailPattern, RegexOptions.Compiled | RegexOptions.IgnoreCase);

                            // Find matches.

                            MatchCollection matches = rx.Matches(line);

                            // Report the number of matches found.

                            int noOfMatches = matches.Count;

                            // Report on each match.

                            foreach (Match match in matches)

                            {

                                writer.Write(match.Value + "\r\n");

                            }

                        }

                    }

                }

            }

            catch (Exception ex)

            {

                Console.WriteLine(ex.Message);

            }

        }

    }

}

Singleton Design Pattern

Singleton Design Pattern

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

namespace WebApplication1

{

    public class Singleton

    {

        // lazy initialization - only object is created first and reference is created when ever required.

        protected static Singleton testobj;

        // Default constructor is made private inorder to stop creating instances for the Singleton class.

        private Singleton()

        {

        }

       // this method will check if the object of the class already exists else it will create and returns it 

        public static Singleton GetObjectReference()

        {

            if (testobj == null)

            {

                testobj = new Singleton();

            }

            return testobj;

        }

        public void Print(string s)

        {

            Console.WriteLine(s);

        }

    }

}

An object reference is required for the nonstatic field method or property in c#

In this Example : Don't make your method (GetObject) static. It doesn't need to be static and it prevents you from using any non-static properties (like testobj). 

However if you need a method to be static, than it should not call the non-static members directly. Because the non-static member variables of a class always belong to an object.

If a method is static than non static members / properties cannot be accessed directly. otherwise create an instance to access non-static members or make the members as static. Else it will throw an error saying "an object reference is required for the nonstatic field method or property in c#" 

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

namespace WebApplication1

{

    public class Singleton

    {

        protected static Singleton _obj;

        private Singleton()

        {

        }

        public static Singleton GetObject()

        {

            if (_obj == null)

            {

                _obj = new Singleton();

            }

            return _obj;

        }

        public void Print(string s)

        {

            Console.WriteLine(s);

        }

    }

}

If static is removed than it errors out as mentioned. Because it cannot access an instance variable.

Understanding Generics

Understanding Generics:

Generics allow you to delay the specification of the data type of programming elements in a class or a method, until it is actually used in the program. In other words, generics allow you to write a class or method that can work with any data type.

namespace Apps

{

    class UnderstandingGenerics

    {

        static void GenericsTest<T>(T lhs, T rhs)

        {

            Console.WriteLine("{0}, {1}", lhs, rhs);

        }

        static void Main(string[] args)

        {

            int a = 10, b = 2;

            Char c = 'r', d = 's';

            GenericsTest<int>(a, b);

            GenericsTest<char>(c, d);

        }

    }

}

HyperLinks in text file C#

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace HyperLinksFilter
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                StreamReader sfilecontent1 = new StreamReader(@"D:\log");
                StreamWriter dfilecontent2 = new StreamWriter(@"D:\test.txt");
                string line;
                while ((line = sfilecontent1.ReadLine()) != null)
                {
                    //string[] words = line.Split(',');
                    //string k = words[1];
                    //dfilecontent2.Write(k.Trim() + "\r\n");

                    if (line.Contains("http"))
                    {
                        dfilecontent2.Write(line+"\r\n"+"\r\n");
                    }
                }
                sfilecontent1.Close();
                dfilecontent2.Close();
                Console.WriteLine("File created Successfully!");
            }
            catch (Exception ex1)
            {
                Console.WriteLine(ex1.Message);
            }
        }
    }
}

Understanding Static Constructor (C# reference)

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace Apps

{

    class statiConstructor

    {

        private static int a;

        static statiConstructor()

        {

            a = 10;

            Console.WriteLine("Static Constructor with static member value=" + a);

        }

        public static void MethodCall()

        {

            Console.WriteLine("Method Call ");

        }

    }

    class UnderstandingStaticConstructor

    {

        public static void Main()

        {

         // In particular, a static constructor is called once, automatically, when the class is used for the first time.

            statiConstructor k = new statiConstructor();

            statiConstructor.MethodCall();
            statiConstructor.MethodCall();

        }

    }

}

Output:

Static Constructor with static member value = 10
Method Call
Method Call