Table method in extension AX 7 / D365 Extend the table in a new method / add a method in standard table in D365

Below is the method created a new method in CustGroup table using extension concept in D365

[ExtensionOf(tableStr(CustGroup))]
Final class TRCustGroup_Extension
{
public Static void method1(CustGroup _custGroup)
{
info(strFmt("Table method using extension , Cust group id %1",_custGroup.CustGroup));
}
}
===========
[ExtensionOf(tableStr(InventTable))]
final class InventTable_Extension
{
    public static boolean isMyFieldEmpty(InventTable _this)
    {
        return _this.MyExtField == '' ? true : false;
    }

}