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Let's start with creating a new Java project.

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I'm going to go to the package explorer area, right click -> New -> Java Project. Let's name it "Simple_TCP" for

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example. Open that, right click on the source package, New -> Package. "simple_tcp". And then I'm going to do

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a right click on that, and create our first class.

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Our class is going to be called "Server", and that's actually going to be all the code we're going to need

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for our server side of our application.

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Now, I'm going to explain every single line of code we use here in a separate lesson, so if you're familiar

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with Java you can just skip that, but for now, I'm going to give you just enough information so that you

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can understand what we're doing here.

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The first thing we're going to do is we're going to create a main method. A main method is an entry point

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to your application, and there's actually a shortcut for this.

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In Java, you just type in "main", press Ctrl + Space,

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press Enter, and there you have it.

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Next, let's add a try-catch block. A try-catch block is basically a piece of code that Java will try to

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run, and then if it fails it's going to go to the catch code.

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So the way you do this - there's also a shortcut for this - you type in "try" and then press Ctrl + Space

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and then press Enter. In the try block,

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I'm going to call new Server();

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Server() is going to be a method - public Server() - where pretty much all of our code is going to be located,

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and then if anything goes wrong in this area here, we're going to be thrown to the catch block.

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And what I want the catch block to do is - I want to use this "e" object.

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That's the exception object.

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And I want it to print out what happens.

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So I want to know what went wrong.

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And that's what I'm going to get by using this method.

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All right.

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Now let's focus on creating sockets.

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On the server side of the application, we're going to have two types of sockets: a server socket and then

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a regular socket. The server socket is just going to hold a port in the operating system for our application.

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And here it goes: we're going to use ServerSocket, and then we're going to name it server_socket.

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server_socket = new ServerSocket

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And then we're going to forward the number of our port.

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I'm going to use 2020.

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Looking into the future here ;) - and I'm going to comment that with "opening a new port". We're getting this

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error because we need to import a packet that contains this ServerSocket method.

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And that packet is java.net.

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But don't worry, there's a shortcut for this too.

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You just need to press Ctrl + Shift + O,

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and here it is - java.net.ServerSocket.

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Now this second error is because we need to throw an exception here

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and we're just going to skip this because I'll explain that later, in this explanatory lesson.

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I'm just gonna use this to avoid the markups that Java shows when when you have an error like that.

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All right. Here I'm going to say "print" - or I'm not gonna do that,

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I'm also going to use a shortcut: "syso" + Ctrl + Shift.

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And there we have System.out.println.

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We're going to print out in the console section, that port 2020 has been opened.

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All right.

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Now we are ready to open this regular communication socket that I've talked about. We're going to use

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the Socket method for it.

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So it's going to be called "socket",

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and we're going to use our ServerSocket, and then call accept(). accept() is a blocking method that accepts

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incoming connections.

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And what a "blocking method" means -

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it means that Java is going to go through our lines of code, and then it's going to stop at this line,

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and it's going to say "OK now I'm waiting for an incoming connection to come up", and it's not going to

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continue to go through the other lines until an incoming connection actually appears and it is accepted.

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Let's quickly import java.net.socket.

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So again, Ctrl + Shift + O should do it.

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There it is.

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Now I'm going to print out a message saying "Client ", and then I'm going to add this client's IP address.

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I'm gonna say socket.getInetAddress(),

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"Inet" is short for Internet.

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And what this method does - it retrieves the client's IP address from the socket object. So socket

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object was created right here, when we got an incoming connection that was accepted.

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So naturally, this object contains information such as - IP address of our client.

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And then I'm going to say "Client " and then their IP address " has connected."

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Now we're going to do something a bit more complex.

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So we're going to create input and output buffers.

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I'm going to add a comment here just to separate this section.

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In this lesson we're just going to go real quick through the code and then I'll explain the details

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later, but for now, you just need to know that we need a place to store our data - the data that is coming

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out of our socket, and the data that is coming into our socket.

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We call that place - a buffer. For the input buffer,

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we're going to use the Buffered Reader.

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And we'll import to these methods or the packets that contain these methods later.

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So, the BufferedReader object is going to be "in_socket", since that's going to read the data that's coming

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into our socket -

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- from the client. new BufferedReader, and then we're going to forward "new InputStreamReader -

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- that's going to read data from the socket.

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So we need to .getInputStream().

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For our outgoing buffer, we're going to use PrintWriter. We're going to name that out_socket = new PrintWriter,

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and then we're going to forward new OutputStreamWriter.

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So here we are actually writing the data into the buffer, and then we're going to go socket dot -

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socket.getOutputStream()

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And here I'm just going to add "true" real quick, and I'll explain what that means

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later, I promise. The only thing left to do here is to import the packets containing these methods,

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and we're going to get that by pressing

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Ctrl + Shift +O

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There we go.

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That's java.io

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java.io

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java.io

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and then all of these methods.

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And now we've got our input and output buffers.

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Now we can actually move on with the code. From this moment on, we are deciding what kind of communication

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we're going to have between our server and our client.

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The first thing I'm going to send as a server is going to be "Welcome!" for example.

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So I'm going to use my out socket, out_socket.println -

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so our client is going to receive this - I'm going to comment this real quick.

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All right.

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And then when I receive the message back from the client, I'm going to store that in a string object.

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I'm going to call that "message", and I'm going to say read from in_socket.

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All right.

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Now, I'm going to print out this message in the console.

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It's going to be

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"Client says:" and then add the message from the client.

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This is going to be our entire client-server communication for now.

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So, after they're done communicating, the only thing left to do is to close the socket.

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So that's what you should always do when the communication is over.

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So once the application is going to shut down, we're going to do "socket.close();"

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I'm going to comment that too, or - it's not going to be a comment but rather a notification in our console.

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I'm going to say "Socket is closed."

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So the purpose of these notifications - as I called them throughout this lesson - is to know when we have

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passed a certain line of code.

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So if we are for any reason stuck in this line, we will never get to this next line.

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So if I get a printout "Socket is closed" in my console, I'm going to know that I've - that Java not me - that

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Java went through this line, and that everything worked correctly, and that now I'm at line twenty nine.

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So this is pretty much it for the server side.

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The next lesson is going to be about the client, and then I'm going to do an explanatory lesson where

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we're going to explain all of these lines of code even further.