Use of modifiedField method in Axapta Tables

1-Create Table with name AutoName

2-Drag and drop ItemId and ItemName EDT from Extended Data Types node in AOT

3- Override modifiedField() in Table's method node.

4- write folling code in method:
public void modifiedField(fieldId _fieldId)
{
       InventTable inventTable;
    ;
   super(_fieldId);

    {
    case fieldNum(AutoName,itemid) :
    {
    this.ItemName = inventTable::find(this.itemid).itemName;
    }
    break;
}
}