Help manipulating Swing default ButtonModel remotely. (NPE on the second client)

[Jibby Lala]

Hi Experts,

I have problem implementing the easy scenario, my intent is to use swing default component's model, so i choose the swing `ButtonModel` for try, i create an instance of model on Server and to update the other models on Clients(local ButtonModel) implement RMI Callbacks.*


The idea is to update the other local `ButtonModel` on clients, when some change happen on the Server shared model but i have problem in implementing this, as i m not finding any realization of such scenario.

This is Client code which should set the button enabled in case of Server button enable by any other Client:

 
    import java.rmi.*;
    import java.rmi.server.UnicastRemoteObject;
    
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    
    import javax.swing.ButtonModel;
    import javax.swing.DefaultButtonModel;
    import javax.swing.JButton;
    import javax.swing.JCheckBox;
    import javax.swing.JLabel;
    import javax.swing.JPanel;
    
    public class ButtonClient extends javax.swing.JFrame implements
    		ICallback {
    
    	private JButton ok;
    	private JLabel enabled;
    
    	private ButtonModel model;
    	static boolean firsttime = true;
    	private Model remoteModel;
    
    	public ButtonClient() {
    
    		try {
    			Remote remoteObject = Naming.lookup("obj");
    
    			if (remoteObject instanceof Model) {
    				remoteModel = (Model) remoteObject;
    
    				remoteModel.register(this);
    				UnicastRemoteObject.exportObject(this);
    
    			} else {
    				System.out.println("Server not a remote Server.");
    				System.exit(0);
    			}
    		} catch (Exception e) {
    			System.out.println("RMI Lookup Exception");
    			System.exit(0);
    		}
    		;
    		java.awt.EventQueue.invokeLater(new Runnable() {
    			public void run() {
    				initComponents();
    			}
    		});
    	}
    
    	private void initComponents() {
    		setTitle("ButtonModel");
    
    		JPanel panel = new JPanel();
    		panel.setLayout(null);
    
    		ok = new JButton("ok");
    		JCheckBox cb = new JCheckBox("Enabled", true);
    
    		ok.setBounds(40, 30, 80, 25);
    
    		cb.addActionListener(new ActionListener() {
    
    			public void actionPerformed(ActionEvent e) {
    				try {
    					if (remoteModel.isEnabled())
    						ok.setEnabled(false);
    					else
    						ok.setEnabled(true);
    				} catch (RemoteException e1) {
    					e1.printStackTrace();
    				}
    			}
    		});
    
    		cb.setBounds(180, 30, 100, 25);
    
    		enabled = new JLabel("Enabled: true");
    		enabled.setBounds(40, 90, 90, 25);
    	
    		panel.add(cb);
    		panel.add(enabled);
    	
    		add(panel);
    
    		setSize(350, 250);
    		setLocationRelativeTo(null);
    		setDefaultCloseOperation(EXIT_ON_CLOSE);
    		setVisible(true);
    
    		model = new mymodel();
    
    		ok.setModel(model);
    
    		panel.add(ok);
    	}
    
    	@Override
    	public void updateClients(Object obj) throws RemoteException {
    
    		if (obj != null) {
    			if (firsttime == false) {
    				if (obj instanceof Boolean) {
    					boolean boo = (Boolean) obj;
    					if (boo) {
    						ok.setEnabled(false);
    						enabled.setText("Enabled: true");
    					} else {
    						ok.setEnabled(true);
    						enabled.setText("Enabled: false");
    					}
    				}
    			} else {
    				firsttime = false;
    			}
    		} else
    			System.err.println("object null exception in updateclient()");
    	}
    
    	class mymodel extends DefaultButtonModel {
    
    		public void setEnabled(boolean b) {
    
    			if (b)
    				enabled.setText("Enabled: true");
    			else
    				enabled.setText("Enabled: false");
    
    			if (firsttime == false) {
    				try {
    					remoteModel.setEnabled(b);
    					System.out.println("calling server model");
    				} catch (RemoteException e) {
    					e.printStackTrace();
    				}
    			} else {
    				firsttime = false;
    				super.setEnabled(b);
    			}
    		}
    	}
    
    	public static void main(String args[]) {
    		new ButtonClient();
    	}
    
    }

This is server site code implementing shared model:

    import java.rmi.*;
    import java.rmi.server.UnicastRemoteObject;
    import java.util.Enumeration;
    import java.util.Vector;
    
    import javax.swing.ButtonModel;
    import javax.swing.DefaultButtonModel;
    
    public class ModelImpl extends UnicastRemoteObject implements Model {
    
    	private boolean msg;
    	public boolean isMsg() {
    		return msg;
    	}
    
    	public void setMsg(boolean msg) {
    		this.msg = msg;
    	}
    
    	private ButtonModel model = new DefaultButtonModel();
    	private static Vector clients = new Vector();
    
    	protected ButtonModelServerImpl() throws RemoteException {
    		super();
    	}
    
    	public void register(ICallback newClient) throws RemoteException {
    		clients.addElement(newClient);
    		System.out.println(clients.size()+"Clients join");
    	}
    
    	public void updateClients(Object obj) throws RemoteException {
    		if (clients != null) {
    			for (Enumeration e = clients.elements(); e.hasMoreElements();) {
    				ICallback client = (ICallback) e.nextElement();
    				try {
    					client.updateClients(obj);
    				} catch (Exception ex) {
    					ex.printStackTrace();
    				}
    			}
    		} else
    			System.err.println("Clientlist is empty");
    	}
    
    	@Override
    	public void setEnabled(boolean b) throws RemoteException {
    		if (isEnabled()){
    			model.setEnabled(false);
    		updateClients(false);}
    		else {
    			model.setEnabled(true);
    			updateClients(true);
    		}
    	}
    
    	@Override
    	public boolean isEnabled() throws RemoteException {
    		return model.isEnabled();
    	}
    }

i would appreciate the concrete implementation of your idea or correction of mine rather then meta discussion.

many thanks,

Jibbylala