Client Implementation

Listing 7.3 (TimecalClient.java)

import java.rmi.*;
import java.net.MalformedURLException;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

//Client implementation
public class TimecalClient extends JFrame{
	
   //instance variables
   private JTextArea txtArea = null;
   private JButton
   btnLocal = null,
   btnRemote =	null;
		
   private TimecalInterface server= null;
	
   //constructor
   public TimecalClient(){
		
	super("Time calculator");
	Container cp = getContentPane();
	
	JPanel btnPanel = new JPanel();
		
	txtArea = new JTextArea(10,50);
		
	//button used to call the remote method
	btnRemote = new JButton("Remote Call");
		
	//button used to call the local method
	btnLocal = new JButton("Local Call");
		
	//listener
	ButtonHandler handler = new ButtonHandler();
		
	btnRemote.addActionListener(handler);
	btnLocal.addActionListener(handler);
	btnPanel.add(btnRemote);btnPanel.add(btnLocal);
	cp.add(txtArea);
	cp.add(btnPanel,BorderLayout.SOUTH);
	
	try{

	  //get a remote reference
	  server = (TimecalInterface)Naming.lookup("Server");
					
	 }catch(RemoteException ex) {
	    txtArea.setText("Error " +ex.getMessage());
	 }
	 catch(MalformedURLException ex) {
	    txtArea.setText("Error " +ex.getMessage());
	 } 
	 catch(NotBoundException ex) {
	    txtArea.setText("Error " +ex.getMessage());
	 } 
	 
	this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
	pack();
	setLocation(10,10);
	show();
 }
	
   //main method
   public static void main(String []client) {
	 new TimecalClient();	
   }
	
   //local method
   private String localCall(String text){
      int i=0;
      for(i=0;i<100;i++)
	System.out.println(text +" "+i);
			
      return text;
}

//Event handling class
private class ButtonHandler 
      implements ActionListener{
      public void actionPerformed(ActionEvent ae){
            JButton temp = (JButton)ae.getSource();
            long before,after;
	 
            if(temp == btnRemote){
			try{
			    before = System.currentTimeMillis();
			    String msg = server.remoteCall("Time taken by remote call:");
			    after = System.currentTimeMillis();
			    msg += after - before; 	
			    txtArea.setText("\n"+ msg);
			   }catch(Exception ex){
	    			txtArea.setText("Error :"+ex.getMessage());
	   		   }
            }
		else{
	 	 
	 	  before = System.currentTimeMillis();
	 	  String msg = localCall("Time taken by local call: ");
		  after = System.currentTimeMillis();
		  msg += after - before; 	
		  txtArea.setText("\n" + msg);
		}
     } 
   }
}

Explanation

The constructor creates a number of components and containers. It creates a TextArea to show messages and two instances of buttons. The remote call button calls the remote method and the local call button calls the local method. It adds event listener to the buttons. Finally, it obtains a reference to the remote object and shows the window. The main method just creates an instance of the Client application. The localCall() method simply returns the string passed to it.

The ButtonHandler class handles the action events generated by the two buttons. It first checks the source of the event and then calls the appropriate method. You can start the application and see the result.

Figure 7.1