Instance variable scope in java

Question

Hello good day to all.

I am creating a networking program in java for my Internet Cafe. I have this code for my server

    import java.io.*;
    import java.net.Socket;
    import java.net.ServerSocket;

public class Server
{
    private String name;
    private int id;

    private Socket socket = null;
    private ServerSocket serversocket = null;
    private ObjectInputStream ois = null;

    public Server()
    {
        new Thread(receive).start();

        while(true)
        {
            try
            {
                serversocket = new ServerSocket(4445);
                socket = serversocket.accept();
                System.out.println("Connected..");
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
        }

    }

    Runnable send = new Runnable(){
        public void run ()
        {

        }

    };

    Runnable receive = new Runnable(){
        public void run ()
        {
            while(true)
            {
                try
                {
                    ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
                    User user = (User) ois.readObject();
                    System.out.println(user);
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
                catch(ClassNotFoundException e)
                {
                    e.printStackTrace();
                }
            }
        }
    };

    public static void main(String [] args)
    {
        new Server();
    }
}

My problem is that I cant access my instance variable inside my Runnable interface code.

For example the "socket" instance. is not accessible inside this code

Runnable receive = new Runnable(){
        public void run ()
        {
            while(true)
            {
                try
                {
                    ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
                    User user = (User) ois.readObject();
                    System.out.println(user);
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
                catch(ClassNotFoundException e)
                {
                    e.printStackTrace();
                }
            }
        }
    };

What is the best approach on this and why is not accessible inside that code?

possible duplicate of Why are only final variables accessible in anonymous class? — m0skit0
– m0skit0, Commented Dec 4, 2014 at 12:32

Community · Accepted Answer · 2017-05-23 12:05:35Z

2

Why? Here is the answer: Why are only final variables accessible in anonymous class?

If you need access to your socket from your server you should declare as a final varible your Socket socket on your Server class.

edited May 23, 2017 at 12:05

CommunityBot

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answered Dec 4, 2014 at 12:28

DavidGSola

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Comments

outdev · Accepted Answer · 2014-12-04 12:27:30Z

1

Try this

public Server() {
    try {
        serversocket = new ServerSocket(4445);
        while (true) {
            socket = serversocket.accept();
            new Thread(receive).start();
            System.out.println("Connected..");
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

answered Dec 4, 2014 at 12:27

outdev

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1 Comment

Yves Gonzaga Over a year ago

Thanks I miss that one

ben3000 · Accepted Answer · 2014-12-04 12:28:42Z

1

If I recall correctly, you need to make the socket field final. The reason escapes me right now.

answered Dec 4, 2014 at 12:28

ben3000

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