C# tip - 7/13/2010

This is one of the most critical tips:
- Prefer coding against interfaces and not abstract classes.

Reasons:

• A way to design by contract.  This way developers will know exactly what the need to implement and consume.
• A way to reuse code.  An object can implement a couple interfaces and the client can call any one of those interfaces to implement that object.

Example 1:

public interface IContact

{

  String name();

  String phoneNumber();

  int id();

}

public class Employee implements IContact

{

  private String name;

  private String phoneNumber;

  private int id;

  public String name(){ return this.name;}

  public String phoneNumber() {return this.phoneNumber}

  public int id() {return this.id;}

  public Employee(id) {this.id = id;}

  public Employee(id,name,phoneNumber)

  {

    this.id = id;

    this.name = name;

    this.phoneNumber = phoneNumber;

  }

  public void DoSomeStuffOnEmployee() {...}

}

public class Employer implements IContact

{

  private String name;

  private String phoneNumber;

  private int id;

  public String name(){ return this.name;}

  public String phoneNumber() {return this.phoneNumber}

  public int id() {return this.id;}

  public Employer(id) {this.id = id;}

  public Employer(id,name,phoneNumber)

  {

    this.id = id;

    this.name = name;

    this.phoneNumber = phoneNumber;

  }

  private int ReturnSomeValue() {...}

  public void DoSomeStuffOnEmployer() {...}

}

public class SomeImplementationClass

{

  public static void DoCrap(IContact contact)

  {

    String name = contact.name();

    String id = contact.id();

  }

}

to call stuff (SHOWS CODE REUSE and DESIGN BY CONTRACT):

public static void main(String[] args)

{

   SomeImplementationClass.DoCrap(new Employee(1));

   SomeImplementationClass.DoCrap(new Employer(5));

   

}

============================

Example 2.

public interface IContact

{

  String name();

  String phoneNumber();

  int id();

}

public interface ICompany

{

  String placeOfWork();

  String address();

}

public class BasePerson implements IContact, ICompany

{

  protected String name;

  protected String phoneNumber;

  protected int id;

  protected String placeOfWork;

  protected String address;

  public String name(){ return this.name;}

  public String phoneNumber() {return this.phoneNumber}

  public String placeOfWork() {..};

  public String address() {..};

  public int id() {return this.id;}

  private Employee( {}

  //code reuse

  protected void DoSomeStuffOn() {...}

}

public class Employer extends BasePerson

{

  public Employer(id) {this.id = id;}

  public Employer(id,name,phoneNumber)

  {

    this.id = id;

    this.name = name;

    this.phoneNumber = phoneNumber;

  }

  private int ReturnSomeValue() {...}

  private void DoSomeStuffOnEmployer() 

  {

    this.DoSomeStuffOn();

  }

}

public class Employee extends BasePerson

{

  public Employee(id) {this.id = id;}

  public Employee(id,name,phoneNumber)

  {

    this.id = id;

    this.name = name;

    this.phoneNumber = phoneNumber;

  }

  private int ReturnSomeValue() {...}

  private void DoSomeStuffOnEmployer()

  {

    this.DoSomeStuffOn();

  }

}

public class SomeImplementationClass

{

  public static void DoCrap(IContact contact)

  {

    String name = contact.name();

    String id = contact.id();

  }

  public static void DoOtherCrap(ICompany contact)

  {

    String placeOfWork= contact.placeOfWork();

  }

}

to call stuff (SHOWS CODE REUSE and DESIGN BY CONTRACT):

public static void main(String[] args)

{

   SomeImplementationClass.DoCrap(new Employee(1));

   SomeImplementationClass.DoOtherCrap(new Employer(5));

   SomeImplementationClass.DoCrap(new Employer(11));

   SomeImplementationClass.DoOtherCrap(new Employee(55));

}