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As promised, in this lesson we're going to make our simple little program a bit more interesting. For

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the sake of keeping our previous code,

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I'm going to create a new packet.

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I'm going to right click on the source packet and go to New -> Package.

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I'm going to name it simple_tcp_2 for example, and then I'm going to copy the previous two classes by

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selecting them, right click -> Copy, and then right click on the simple_tcp_2 package, and then Paste. I'm

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going to close the previous two classes and open the two new ones.

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The first thing we're going to change is - we're going to enable the client to be able to send something

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custom to the server instead of just saying "Thanks". We're going to need a Scanner for this. I'm going

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to create a new Scanner

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right here. It's going to be Scanner -

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for example, "keyboard" - new scanner - and then we're going to use System input.

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Then I'm just gonna press Ctrl + Shift +O to import all the necessary packages. And now we need to prompt

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the user to type something in. I'm going to say System.out, but I'm not going to use "println", I'm just

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going to use "print".

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The difference is that this one doesn't add a new line after the text. So the prompt is going to say

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"Say something to the server: " for example, and then the user is now supposed to type something in.

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So I'm going to use the message String.

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All right.

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That should be it.

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So we're here we're prompting the user to say something - to type something in - to be sent to the server,

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and then whatever they type in, it is going to be stored in the message String and then that's what we're

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going to send out instead of "Thanks!"

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It's just going to be "message".

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All right, let's save this and then run it to see if it works.

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I'm going to go to the server and I'm going to run the server. And then I'm going to run the client.

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And here we can see the prompt.

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So I'm going to type in - instead of "Thanks" - let's just say "Ok, whatever"

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I'm going to press Enter. And on the server side - in the server console - we can see that this is the message

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that we've received.

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And then the socket is closed.

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That was pretty simple.

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I'm going to clean this up and now we're going to complicate things a bit further.

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What we're going to do now is - we're going to play a simple game. We'll generate a random number between

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1 and 10 on the server, and then we're going to ask the client to guess the number.

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First, I'm going to clean up a little bit in the Client class.

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So we're going to need this string,

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and I'm not actually going to need any of this.

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So this is where our new code is going to be at,

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and then I'm going to go to the server. Over here we're also going to need the string - or are we? - We're

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not, we're actually going to need an integer here. So I'm just going to delete all of this

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and I'm going to start by generating a random number.

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It's going to be an integer and I'm going to call it secret_number.

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Now this is just one of the ways you can do this.

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I'm going to use the Random() method.

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What this means is - give me a random number out of the first 10 numbers - but always remember that we as

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engineers, and especially if you're a programmer - you always count from zero.

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So this would actually return a random number between 0 and 9.

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So in order to get a number between 1 and 10, we're just going to add 1 to whatever this returns. Next,

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we're going to use a do-while loop.

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If you are a total beginner to programming, just a short explanation here: a do-while loop lets you run

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through the loop at least once.

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That means we only check the condition to go into the loop at the end of the first run.

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So you actually have to go through the code at least once to get to the condition.

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I'm going to say do -

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and then we're going to prompt the user to guess a number right away.

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So we're going to use the out_socket for that. out_socket.println - and then we're going to send "Guess

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"Guess a number from 1 to 10: "

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Next,

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we're expecting a message back from the client.

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OK.

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So it turns out I am going to need that string after all - so the message is going to come through the

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socket.

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It's going to be in_socket.readLine()

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in_socket.readLine()

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and now let me define that string.

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All right.

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So what we have here is the first time we run into this code - into this loop

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in particular - we are going to send a message to the client saying "Guess a number from 1 to 10", and then

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we're expecting a message back from the client, where in this message we have a number.

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So what we're going to have to do is - we're going to have to translate that message - which is a string -

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OK as long as we use this readLine() method,

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we're going to be getting a string.

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Now this is a number, so I have to translate that number from a string to an integer.

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I'll do this within the while condition.

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So I'm going to say - all right -

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Now bear with me: integer.parseInt(message) - and we're going to compare that to secret_number, but we need

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that to be not equal to our secret_number.

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that to be not equal to our secret_number.

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Let me try and explain this a bit better.

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So, as long as this condition is met, and this is pretty much saying: "OK so this is what the client is

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giving us, and as long as they're not hitting the right number, we need to go back into the loop."

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We need to say "Guess a number"

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again. That means that they haven't got the right number yet.

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So we keep sending them the prompt and the opportunity to guess the number once more. For the first time

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when they hit the right number -

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- so when they type in the exact number that we have generated here - we're going to get out of this loop.

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When we do get out of the loop,

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we're going to send out_socket.println("You got it!!!") - for example. You can send whatever you want.

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And then I'm going to print out in the servers console "Secret number is out." - for example - "Exiting the

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app." - that's hopefully it for the server,

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I'm going to save this and switch to the client. The client is going to be guessing a number. I'm going

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to call that "user_number", and we're going to be creating a loop here too.

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It's going to be a regular while loop, and the condition is going to be: read from the in_socket,

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in_socket.readln, and then if that line starts with "Guess",

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that means we haven't guessed the number yet, and we're getting into the loop. As long as we're in the

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loop,

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We're going to be printing out a prompt saying - for example, "Servers says:

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Guess a number from 1 to 10."

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and then we're going to prompt our user to type in a number.

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We're going to store whatever they type in into our user_number string.

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We're going to store whatever they type in into our user_number string.

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And we're going to simply just send out that string to the server.

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We're going to use the out_socket for that.

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We're just going to say println(user_number).

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As long as we send the wrong number,

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we will be getting a message back, saying "Guess a number."

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So this condition will be met as long as we're hitting the wrong number, and we will keep going through

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this loop.

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So as long as we're getting a sentence beginning with a "Guess", we need to be in this loop. As soon as

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we get something else,

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the other thing we can get is "You got it!!!" -

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- we are going to fall out of our loop.

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So we're just going to print out when that happens. Obviously, right after this bracket, we're out of the

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loop and we can print out:

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"You got it!!!". Let's save this and see if it works.

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As always, I'm going to run the server first, and then I'm going to run the client.

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Ok, let's play the game. So the server is saying - you need to make sure that you're in the client console

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window - so the server is saying "Guess a number." - I'm going to try 1, I haven't got it yet, so I'm going to just

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go from 1 to 10, I'm going to 2,

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3, 4, 5, 6 - and I got it!

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It's 6. Of course, as soon as you get the right number the next line of code for both the client and the

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server is going to be socket.close(). So the socket is going to be closed right after we get this message

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that we have hit the right number.

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Now this was very basic but hopefully it got you interested to continue to play around with the code.

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If you have any questions or issues send me a message or just post it in the Q&A section!