private void btnCalculateActionPerformed(java.awt.event.ActionEvent evt) {
            SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MMMM-yyyy, hh:mm:ss");
            Date date = new Date();
            String basicSalary = fmtBasic.getText();
            double basic = 0.00;
            double hours = (Double)spnHours.getValue();
            String department = (String)cboDept.getSelectedItem();
            String id = fmtId.getText();
            String name = txtName.getText();
            double total = 0.00;
            double rate = 0.00;

		if( fmtId.getText().trim().length() != 4 ){
			// tarMessage.setText("Invalid input(s)\n\n");
			tarMessage.append("-[Staff ID must not empty]\n");
		}else if( txtName.getText().trim().length() < 4 || txtName.getText().trim().length() > 20 ){
			tarMessage.append("-[Name] must not more than 20 chars\n");
		}else if( cboDept.getSelectedIndex() == 0 ){
			tarMessage.append("-[Department] must be selected\n");
		}else if( fmtBasic.getText().trim().length() < 1 ){
			tarMessage.append("-[Basic Salary] must not empty\n");
		}else{
			basic = Double.parseDouble( fmtBasic.getText() );
			if( basic < 1000 || basic > 5000 ){
				tarMessage.append("[Basic Salary] must be between RM1000 - RM5000\n");
			}else{
				// calculate salary
				if( hours <= 20 ){
					rate = 20.00 * hours;
				}else{
					rate = (20.00 * 20) + 30.00 * (hours - 20);
				}
				total = basic + rate;

				tarMessage.setText("Salary for Mr. " + name + " (" + id + ")\n"
								+ "from " + department + ":\n\n"
								+ "Basic Salary = RM " + basic + "\n"
								+ "OT Claims = RM " + hours + "\n"
								+ "Total Salary = RM " + total + "\n\n"
								+ "As on " + dateFormat.format( date) );

				error = false;

			}
		}
	error = true;
}