//class used to handle action events generated by the buttons.
  private class ButtonHandler 
	implements ActionListener{

    //Invoked when a user clicks a button.
    public void actionPerformed(ActionEvent ae){
			
	//Get the object on which the Event 
	//initially occurred.
	JButton temp = (JButton)ae.getSource();
			
	//Get the action command for this button.
	String actionCommand = temp.getActionCommand();
			
	try{
			
	  //if add button is clicked 
	  //call the add method
  	  if(actionCommand.equals("Add"))
		 add();
			
	  //if Update button is clicked 
	  //all the update method
	  else if(actionCommand.equals("Update"))	 
		 update();
			
	  //if Delete button is pressed 
	  //call the delete method
  	  else if(actionCommand.equals("Delete"))	 
		 delete();
			
	  //if Clear button is clicked 
	  //call the clear method
  	  else if(actionCommand.equals("Clear"))	 
		 clear();
			
	  //if Find button is clicked 
	  //call the find method
	  else if(actionCommand.equals("Find"))	 
		 find();
			 
	}catch(Exception ex){
		showMessageDialog(ex.getMessage());
		 
	}
   }
		
    //method invoked when add button is pressed
   private void add()
	throws RemoteException,SQLException{
								
	//Check whether the form is properly filled or not.
	if(check()){
		showMessageDialog(
		  "Please fill complete information.");
		return;
	}
									
	//Parse the string argument.
	int rollno = Integer.parseInt(txtRollNumber.getText());
	
	//Get the name of student
	String name = txtName.getText();
			
	//Get the course
	String course = txtCourse.getText();

	//create a student object 
	//with specified roll no,
	//name and course.
	Student std = new Student(rollno,name,course); 

	//Call the remote method to add 
	//a new student record
	String res = server.addRecord(std);
	
	//Clear all text boxes
	clear();		

	//Show the message returned by the server.
	showMessageDialog(res);
     }
	 
    //method invoked when update button is pressed
    private void update()
	throws RemoteException,SQLException{
			
	//Check whether the form is properly filled or not.
	if(check()){
		showMessageDialog(
		  "Please fill complete information.");
		return;
	 }
						
	//get the roll number
	int rollno = Integer.parseInt(txtRollNumber.getText());
			
	//get the name
	String name = txtName.getText();
			
	//get the course
	String course = txtCourse.getText();
			
	//create a student object with specified roll no,
	//name and course.
	Student std = new Student(rollno,name,course);

	//call the remote method to update 
	//the record.
	String res = server.updateRecord(std);		

	//clear values in the text boxes
	clear();

	//Show the message returned by the server.
	showMessageDialog(res);
   }
	 
   //Method invoked when Delete button is pressed
   private void delete()
	throws RemoteException,SQLException{
			
	 //get the roll number
	 String value = txtRollNumber.getText().trim();	 		 	 	
 	 if(value.equals("")){
	 	 	 
 	   //if roll number is not entered
	   showMessageDialog("Please enter the Roll number.");
	   return;
	 }
		 
	 //Parse the string argument.
	 int rollno = Integer.parseInt(txtRollNumber.getText());
		 		
	 //Call the remote method to delete the record.
	 String res = server.deleteRecord(rollno);

	//Clear the text boxes.
	clear();
	
	//Show message returned by the server.
	showMessageDialog(res);
   }
	 
	 
    //method invoked when Clear button is pressed
     private void clear(){
 	
	//set the text of all the text boxes.
 	txtRollNumber.setText("");
 	txtName.setText("");
 	txtCourse.setText("");
    }
	
    //method to find a record
    private void find()
	 throws RemoteException, SQLException{
	 	
	//Get the Roll number of student.
 	String value = txtRollNumber.getText().trim();	 		 	 	
	 	
 	if(value.equals("")){
	 		
 	  //if roll number is not entered
  	  showMessageDialog("Please enter the Roll number.");
	  return;
	}
		
	int rollno = Integer.parseInt(txtRollNumber.getText());
	 	
	// Call the remote method to search the record.
 	Object res = server.findRecord(rollno);

	//If a string is returned by server.
	if(res instanceof String){
	  String temp = (String)res;
	  showMessageDialog(temp);
	  clear();
	}
	else{
	   Student temp = (Student)res;
	 
	 //method to fill text boxes with values.
	 fill(temp);
	}
   }
	 
   //Check whether values are filled or not,
    private boolean check(){

	boolean value = txtRollNumber.getText().trim().equals("") ||  
	txtName.getText().trim().equals("")||
	txtCourse.getText().trim().equals("");	
 	
	return value;	 
    }
	
   //fill the text boxes.
   private void fill(Student std){

	txtName.setText(std.getName());
	txtCourse.setText(std.getCourse());
   }
	 
  //method used to show a dialog box.
    private void showMessageDialog(String msg){
	JOptionPane.showMessageDialog(null,msg
 	,"INFORMATION",JOptionPane.INFORMATION_MESSAGE);
    }
	 
  }
}