Provide a hint in NotConnectedException

that connect() needs to be called prior login().

SMACK-686

smack-core/src/main/java/org/jivesoftware/smack/AbstractXMPPConnection.java

@@ -403,7 +403,7 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
      */
     public synchronized void login() throws XMPPException, SmackException, IOException {
         if (isAnonymous()) {
-            throwNotConnectedExceptionIfAppropriate();
+            throwNotConnectedExceptionIfAppropriate("Did you call connect() before login()?");
             throwAlreadyLoggedInExceptionIfAppropriate();
             loginAnonymously();
         } else {
@@ -584,8 +584,12 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
     }
 
     protected void throwNotConnectedExceptionIfAppropriate() throws NotConnectedException {
+        throwNotConnectedExceptionIfAppropriate(null);
+    }
+
+    protected void throwNotConnectedExceptionIfAppropriate(String optionalHint) throws NotConnectedException {
         if (!isConnected()) {
-            throw new NotConnectedException();
+            throw new NotConnectedException(optionalHint);
         }
     }
 

smack-core/src/main/java/org/jivesoftware/smack/SmackException.java

@@ -1,6 +1,6 @@
 /**
  *
- * Copyright 2014 Florian Schmaus
+ * Copyright 2014-2015 Florian Schmaus
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -152,7 +152,12 @@ public class SmackException extends Exception {
         private static final long serialVersionUID = 9197980400776001173L;
 
         public NotConnectedException() {
-            super("Client is not, or no longer, connected");
+            this(null);
+        }
+
+        public NotConnectedException(String optionalHint) {
+            super("Client is not, or no longer, connected."
+                            + (optionalHint != null ? ' ' + optionalHint : ""));
         }
     }