Java: How to Create Interface

[rynox]

I'm working on a multi-threaded server project and I created two classes:

1. Class that will open a server socket and loop through accepting sockets. Each time it accepts a connection it spawns a new thread on class #2.

2. This class, in the run() method will create an inputstream from the server socket and read each line coming through the server socket.

What I want to do is in CLASS #1 implement an interface that will invoke a certain method in class #1 each time a line is entered in the server socket. How do you do this?

Here is condensed class #1:

public Library() {
	ServerSocket serverSocket=null;
	boolean listening=true;
	try {
		serverSocket=new ServerSocket(801);
		while(listening) new rServer(serverSocket.accept()).start();
		serverSocket.close();
	} catch(Exception e) { System.exit(0); }
}
static public void main(String[] args) { new Library(); }
public void processCommand(String cmd, Thread thread){ }

Here is the run() method of class #2.

public void run() {
	try {
		DataInputStream in=new DataInputStream(s.getInputStream());
		DataOutputStream out=new DataOutputStream(s.getOutputStream());
		out.writeChars("Number of connections: ");
		out.writeChars(java.lang.String.valueOf(Thread.activeCount()-2)+"\r\n");
		String line=null;
		while(true) {
			Thread.yield();
			line=in.readLine();
			System.out.print("Thread ");
			System.out.print(Thread.currentThread());
			System.out.println(" :" + line);
			command(line);
			if(line.equalsIgnoreCase("exit")) {
				s.close();
				Thread.currentThread().stop();
			}
		}
	} catch(Exception e) {
		System.out.println(e.getMessage());
	}
}

See everything works, I just want to invoke method processCommand(String,Thread) each time a line comes in. I think I need to create an interface and implement on class #1, but I've never done that before. How?

[rynox]

Solved, guess I was barking up the wrong tree with the interfaces, I really needed to create an abstract class. Here's what I did.

I created an abstract class:

public abstract class rServerCommands {
	public abstract void command(String cmd,Thread thr);
}

Then, in my first class I extened the abstract class:

public class Library extends rServerCommands {...
 ...while(listening) new rServer(serverSocket.accept(),this).start();

Then, in the constructor of class 2:

public rServer(Socket s, rServerCommands obj) {...
...
obj.command(...

This way the main class, class 1, can pass itself as an argument to class 2. Since class 1 is a subclass of abstract rServerCommands, class 2 doesn't need to know what class it is, just that it is a rServerCommands class and can invoke the method command(String...etc).