what are predefined methods that cannot be overrided in c#

Any built-in methods which is not virtual can't override. Below is some part of the built-in class DataTable definition.

//
// Summary:
// This method returns an System.Xml.Schema.XmlSchemaSet instance containing the
// Web Services Description Language (WSDL) that describes the System.Data.DataTable
// for Web Services.
//
// Parameters:
// schemaSet:
// An System.Xml.Schema.XmlSchemaSet instance.
//
// Returns:
// The System.Xml.Schema.XmlSchemaSet instance.
public static XmlSchemaComplexType GetDataTableSchema(XmlSchemaSet schemaSet);
//
// Summary:
// Commits all the changes made to this table since the last time System.Data.DataTable.AcceptChanges
// was called.
public void AcceptChanges();
//
// Summary:
// Begins the initialization of a System.Data.DataTable that is used on a form or
// used by another component. The initialization occurs at run time.
public virtual void BeginInit();
//
// Summary:
// Turns off notifications, index maintenance, and constraints while loading data.
public void BeginLoadData();
//
// Summary:
// Clears the System.Data.DataTable of all data.
public void Clear();
//
// Summary:
// Clones the structure of the System.Data.DataTable, including all System.Data.DataTable
// schemas and constraints.
//
// Returns:
// A new System.Data.DataTable with the same schema as the current System.Data.DataTable.
public virtual DataTable Clone();
//
// Summary:
// Computes the given expression on the current rows that pass the filter criteria.
//
// Parameters:
// expression:
// The expression to compute.
//
// filter:
// The filter to limit the rows that evaluate in the expression.
//
// Returns:
// An System.Object, set to the result of the computation. If the expression evaluates
// to null, the return value will be System.DBNull.Value.
public object Compute(string expression, string filter);
//
// Summary:
// Copies both the structure and data for this System.Data.DataTable.
//
// Returns:
// A new System.Data.DataTable with the same structure (table schemas and constraints)
// and data as this System.Data.DataTable.If these classes have been derived, the
// copy will also be of the same derived classes. System.Data.DataTable.Copy creates
// a new System.Data.DataTable with the same structure and data as the original
// System.Data.DataTable. To copy the structure to a new System.Data.DataTable,
// but not the data, use System.Data.DataTable.Clone.
public DataTable Copy();
//
// Summary:
// Returns a System.Data.DataTableReader corresponding to the data within this System.Data.DataTable.
//
// Returns:
// A System.Data.DataTableReader containing one result set, corresponding to the
// source System.Data.DataTable instance.
public DataTableReader CreateDataReader();
//
// Summary:
// Ends the initialization of a System.Data.DataTable that is used on a form or
// used by another component. The initialization occurs at run time.
public virtual void EndInit();
//
// Summary:
// Turns on notifications, index maintenance, and constraints after loading data.
public void EndLoadData();
//
// Summary:
// Gets a copy of the System.Data.DataTable containing all changes made to it since
// it was last loaded, or since System.Data.DataTable.AcceptChanges was called,
// filtered by System.Data.DataRowState.
//
// Parameters:
// rowStates:
// One of the System.Data.DataRowState values.
//
// Returns:
// A filtered copy of the System.Data.DataTable that can have actions performed
// on it, and later be merged back in the System.Data.DataTable using System.Data.DataSet.Merge(System.Data.DataSet).
// If no rows of the desired System.Data.DataRowState are found, the method returns
// null.
public DataTable GetChanges(DataRowState rowStates);
//
// Summary:
// Gets a copy of the System.Data.DataTable that contains all changes made to it
// since it was loaded or System.Data.DataTable.AcceptChanges was last called.
//
// Returns:
// A copy of the changes from this System.Data.DataTable, or null if no changes
// are found.
public DataTable GetChanges();
//
// Summary:
// Gets an array of System.Data.DataRow objects that contain errors.
//
// Returns:
// An array of System.Data.DataRow objects that have errors.
public DataRow[] GetErrors();
//
// Summary:
// Populates a serialization information object with the data needed to serialize
// the System.Data.DataTable.
//
// Parameters:
// info:
// A System.Runtime.Serialization.SerializationInfo object that holds the serialized
// data associated with the System.Data.DataTable.
//
// context:
// A System.Runtime.Serialization.StreamingContext object that contains the source
// and destination of the serialized stream associated with the System.Data.DataTable.
//
// Exceptions:
// T:System.ArgumentNullException:
// The info parameter is a null reference (Nothing in Visual Basic).
public virtual void GetObjectData(SerializationInfo info, StreamingContext context);

You can see some methods are defined as virtual and can be overriden like below. e.g. clone().

public class Car : DataTable
{
public override DataTable Clone()
{
//your logic
return base.Clone();
}
}

Methods defined as non virtuals can't override. The list is huge, but in VisualStudio, you can check is it virtual or not.

2 Replies

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Jaish Mathews8y ago
Any built-in methods which is not virtual can't override. Below is some part of the built-in class DataTable definition.
//
    // Summary:
    //     This method returns an System.Xml.Schema.XmlSchemaSet instance containing the
    //     Web Services Description Language (WSDL) that describes the System.Data.DataTable
    //     for Web Services.
    //
    // Parameters:
    //   schemaSet:
    //     An System.Xml.Schema.XmlSchemaSet instance.
    //
    // Returns:
    //     The System.Xml.Schema.XmlSchemaSet instance.
    public static XmlSchemaComplexType GetDataTableSchema(XmlSchemaSet schemaSet);
    //
    // Summary:
    //     Commits all the changes made to this table since the last time System.Data.DataTable.AcceptChanges
    //     was called.
    public void AcceptChanges();
    //
    // Summary:
    //     Begins the initialization of a System.Data.DataTable that is used on a form or
    //     used by another component. The initialization occurs at run time.
    public virtual void BeginInit();
    //
    // Summary:
    //     Turns off notifications, index maintenance, and constraints while loading data.
    public void BeginLoadData();
    //
    // Summary:
    //     Clears the System.Data.DataTable of all data.
    public void Clear();
    //
    // Summary:
    //     Clones the structure of the System.Data.DataTable, including all System.Data.DataTable
    //     schemas and constraints.
    //
    // Returns:
    //     A new System.Data.DataTable with the same schema as the current System.Data.DataTable.
    public virtual DataTable Clone();
    //
    // Summary:
    //     Computes the given expression on the current rows that pass the filter criteria.
    //
    // Parameters:
    //   expression:
    //     The expression to compute.
    //
    //   filter:
    //     The filter to limit the rows that evaluate in the expression.
    //
    // Returns:
    //     An System.Object, set to the result of the computation. If the expression evaluates
    //     to null, the return value will be System.DBNull.Value.
    public object Compute(string expression, string filter);
    //
    // Summary:
    //     Copies both the structure and data for this System.Data.DataTable.
    //
    // Returns:
    //     A new System.Data.DataTable with the same structure (table schemas and constraints)
    //     and data as this System.Data.DataTable.If these classes have been derived, the
    //     copy will also be of the same derived classes. System.Data.DataTable.Copy creates
    //     a new System.Data.DataTable with the same structure and data as the original
    //     System.Data.DataTable. To copy the structure to a new System.Data.DataTable,
    //     but not the data, use System.Data.DataTable.Clone.
    public DataTable Copy();
    //
    // Summary:
    //     Returns a System.Data.DataTableReader corresponding to the data within this System.Data.DataTable.
    //
    // Returns:
    //     A System.Data.DataTableReader containing one result set, corresponding to the
    //     source System.Data.DataTable instance.
    public DataTableReader CreateDataReader();
    //
    // Summary:
    //     Ends the initialization of a System.Data.DataTable that is used on a form or
    //     used by another component. The initialization occurs at run time.
    public virtual void EndInit();
    //
    // Summary:
    //     Turns on notifications, index maintenance, and constraints after loading data.
    public void EndLoadData();
    //
    // Summary:
    //     Gets a copy of the System.Data.DataTable containing all changes made to it since
    //     it was last loaded, or since System.Data.DataTable.AcceptChanges was called,
    //     filtered by System.Data.DataRowState.
    //
    // Parameters:
    //   rowStates:
    //     One of the System.Data.DataRowState values.
    //
    // Returns:
    //     A filtered copy of the System.Data.DataTable that can have actions performed
    //     on it, and later be merged back in the System.Data.DataTable using System.Data.DataSet.Merge(System.Data.DataSet).
    //     If no rows of the desired System.Data.DataRowState are found, the method returns
    //     null.
    public DataTable GetChanges(DataRowState rowStates);
    //
    // Summary:
    //     Gets a copy of the System.Data.DataTable that contains all changes made to it
    //     since it was loaded or System.Data.DataTable.AcceptChanges was last called.
    //
    // Returns:
    //     A copy of the changes from this System.Data.DataTable, or null if no changes
    //     are found.
    public DataTable GetChanges();
    //
    // Summary:
    //     Gets an array of System.Data.DataRow objects that contain errors.
    //
    // Returns:
    //     An array of System.Data.DataRow objects that have errors.
    public DataRow[] GetErrors();
    //
    // Summary:
    //     Populates a serialization information object with the data needed to serialize
    //     the System.Data.DataTable.
    //
    // Parameters:
    //   info:
    //     A System.Runtime.Serialization.SerializationInfo object that holds the serialized
    //     data associated with the System.Data.DataTable.
    //
    //   context:
    //     A System.Runtime.Serialization.StreamingContext object that contains the source
    //     and destination of the serialized stream associated with the System.Data.DataTable.
    //
    // Exceptions:
    //   T:System.ArgumentNullException:
    //     The info parameter is a null reference (Nothing in Visual Basic).
    public virtual void GetObjectData(SerializationInfo info, StreamingContext context);
You can see some methods are defined as virtual and can be overriden like below. e.g. clone().
public class Car : DataTable
    {
        public override DataTable Clone()
        {
                     //your logic
            return base.Clone();
        }

}
Methods defined as non virtuals can't override. The list is huge, but in VisualStudio, you can check is it virtual or not.
+1
Nanddeep Nachan8y ago
Specifying methods as virtual, abstract, or override make them overriden
Absense of these means a method is final.
+1