java null pointer from another class - user-interface

Question

I have 2 classes one called Gui and one called Listener.
The code for Listener is :
package app.assignment.u0961036.core;
import net.jini.space.JavaSpace;
public class Listener extends Thread {
private JavaSpace space;
private Gui list;
public void run() {
space = SpaceUtils.getSpace("localhost");
System.out.println("In Listener");
int i = 0;
while(true){
i++;
try{
Message mTemplate = new Message();
System.out.println("Listner: template created");
Message nextMessage = (Message)space.take(mTemplate,null,Long.MAX_VALUE);
System.out.println("Listner: Message created");
String message = nextMessage.message;
System.out.println("Listner: message= "+message);
list.newMessage(message);
} catch ( Exception e) {
e.printStackTrace();
}
if(i % 10 == 0){
System.out.println("I = "+i);
}
}
}
public static void listen() {
(new Listener()).start();
}
The relevant code in Gui is:
public void newMessage(String message){
System.out.println("in new message");
chatTextArea.append(" Someone Says: " + message + "\n" );
}
When The code in Listener is run I get a null pointer from the following line:
list.newMessage(message);
I'm not sure why because the object is created.
The GUI is also created win the Gui class if you haven't already guessed.
any Ideas?

Answer 1

package app.assignment.u0961036.core;
import net.jini.space.JavaSpace;
public class Listener extends Thread {
private JavaSpace space;
space = new JavaSpace();
private Gui list;
list = new Gui();
public void run() {
space = SpaceUtils.getSpace("localhost");
System.out.println("In Listener");
int i = 0;
while(true){
i++;
try{
Message mTemplate = new Message();
System.out.println("Listner: template created");
Message nextMessage = (Message)space.take(mTemplate,null,Long.MAX_VALUE);
System.out.println("Listner: Message created");
String message = nextMessage.message;
System.out.println("Listner: message= "+message);
list.newMessage(message);
} catch ( Exception e) {
e.printStackTrace();
}
if(i % 10 == 0){
System.out.println("I = "+i);
}
}
}
public static void listen() {
(new Listener()).start();
}
The code above should fix your problem I think. In Java you create Objects by declaring and instantiating and initialising them. Read here for more information.