Re: Java symbol confusion

From:

"Oliver Wong" <owong@castortech.com>

Newsgroups:

comp.lang.java.help

Date:

Mon, 23 Oct 2006 14:18:46 GMT

Message-ID:

<ab4%g.35789$P7.7350@edtnps89>

[post re-ordered]

"Constant Meiring" <icesslinux@gmail.com> wrote in message
news:1161603400.648663.197940@m7g2000cwm.googlegroups.com...

Matt Humphrey wrote:

"Constant Meiring" <icesslinux@gmail.com> wrote in message
news:1161127462.963642.75210@i42g2000cwa.googlegroups.com...

I started learning myself java a while ago and there's still loads of
concepts and things about the java language i don't know, so i may just
make an arse of myself now...

[...]

my first problem here is that when the two lines marked with arrows
above is out of the try-catch block, NetBeans tells me it can't find
the symbol serverSocket. On the other hand, when I put the two marked
lines inside of the try-catch block, it works without a problem. Can
someone explain to me why this is happening??

The name "serverSocket" is a local variable and that name exists only
from
the { of the try to the } before the catch. After that } the name no
longer
exists, so you can't use it within the catch expression or afterwards.
Put
ServerSocket = null; before the try { and remove the ServerSocket
declaration. The name will then exist for the entire method body.

Thanx now I know why you have to put an object = null sometimes.

    You only ever need to put an object = null if you actually want that
object to be null. If you want to declare a variable to exist at a certain
scope level, but not assign to it, you can do that too:

public class Main {
  public static void main(String[] args) {
    ServerSocket serverSocket; /*Don't assign any value to it yet.*/
    try {
      serverSocket = new ServerSocket(56);
    } catch (IOException e) {
      System.out.println("Couldn't create server socket. Aborting.");
      System.exit(-1);
    }
    clientSocket = serverSocket.accept(); /*presumably, clientSocket was
declared somewhere*/
  }
}

    - Oliver