Populate datagrid from arraycollection of object

// empCollection arrayCollection
[Bindable]
public var empCollection:ArrayCollection;
 
// add employee function
public function addEmployee():void
{
	var anEmployee:Employee = new Employee( firstNameInput.text, lastNameInput.text, departmentList.text, phoneInput.text )
	this.empCollection.addItem( anEmployee );
	Alert.show ( String( this.empCollection ), "New Employee" );
	clearInput();
}
 
// datagrid
<mx:DataGrid x="10" y="10" id="empDg" width="486" dataProvider="{empCollection}">
	<mx:columns>
		<mx:DataGridColumn headerText="First Name" dataField="firstName"/>
		<mx:DataGridColumn headerText="Last Name" dataField="lastName"/>
		<mx:DataGridColumn headerText="Department" dataField="departmentDf"/>
		<mx:DataGridColumn headerText="Phone" dataField="phoneDf"/>
	</mx:columns>
</mx:DataGrid>
 
// Employee.as
package
{	
	public class Employee
	{
		
		public function Employee( aFirstName:String, aLastName:String, aDepartment:String, aPhone:String ):void
		{
			this.firstName = aFirstName;
			this.lastName = aLastName;
			this.department = aDepartment;
			this.phone = aPhone;
		}
		
		public function getFirstName():String
		{
			return this.firstName;
		}
		
		public function getLastName():String
		{
			return this.lastName;
		}
		
		public function toString():String
		{
			return this.firstName + " " + this.lastName + " " + this.department + " " + this.phone;
		}
		
		private var firstName:String;
		private var lastName:String;
		private var department:String
		private var phone:String;
		
	}
}