Chapter 15: How to Work with Interfaces and Generics

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Philomena Cook
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1 CIS 260 C# Chapter 15: How to Work with Interfaces and Generics 1. Introduction An interface: a set of signatures without implementation for one or more methods, properties, indexers or events. Any class that implements the interface must provide implementation of the members of the interface. Naming convention: the names of interfaces start with capital I. The name of the interface must be included in the class declaration that implements the interface: e.g. public class Product : IDisplayable Any object of the class product is also an object of the interface IDisplayable. A class may implement two or more interfaces. A class may inherit another class and implement several interfaces. Syntax for a class that inherits another base class and implements several interfaces: public class ClassName : BaseClass, Interface1, Interface2 Interfaces and Abstract Classes Both interfaces and abstract classes provide signatures for properties and methods that a class must implement. All of the members of an interface are abstract. In contrast, an abstract class can implement some or all of its members. A class can inherit only one class (including abstract classes), but a class can implement more than one interface. Interfaces can t declare static members, but abstract classes can. 1

2 2. Some interfaces defined in.net Commonly used.net interfaces Interface ICloneable IComparable IConvertible IDisposeable Members object Clone() int CompareTo(object) TypeCode GetTypeCode() decimal ToDecimal() int ToInt32() (etc.) void Dispose() Fig on p. 463 lists some interfaces for collections 3. How to create an interface Syntax: public interface InterfaceName type MethodName(parameters); // Declares a method type PropertyName [get;] [set;]... // Declares a property // Declares a get accessor // Declares a set accessor All interface members are public and abstract. That is why the keywords public and abstract are not used in the interface declaration. Interfaces cannot define static members All declaration inside the interface end with semicolon ;. An interface can inherit other interfaces. The class that implements such interface must implement all members of the inherited interfaces 2

3 Example: public interface IDataAccessObject : IDisplayable, IPersistable // add additional members here Coding an interface Project Add New Item Interface 4. How to implement an interface After the name of the interface is entered on a class declaration, right-click on the name and select the Implement Interface command to generate stubs for the members of the interface. The Explicitly Implement Interface command is used when: a) There might be ambiguity due to implementing several interfaces b) The implemented members are not public c) The implemented members should not be virtual or abstract. 5. Using objects with interface type as parameters When we have an object of some class that implements some interface, and we want to have a method that applies the interface methods to that object, the parameter that receives the object has to be with the interface as its type. Example public static List<object> CreateList(ICloneable obj, int count) List<object> objects = new List<object>(); for (int i = 0; i < count; i++) object o = obj.clone(); objects.add(o); return objects; 3

4 The CreateList method does not know what the type of the parameter obj is, it only knows that obj can be cloned. 6. How to work with generic types Very often we need classes whose functionality does not depend on the type if the objects that they process. For example, queues, stacks, lists, arrays can have any type of objects. Generic types are defined by <T> following the name of the type. When the type is used, T is replaced with the particular type that is needed in the application. Example: public class CustomList<T> private List<T> list = new List<T>(); // an Add method public void Add(T item) list.add(item); // a read-only indexer public T this[int i] get return list[i];.. Ussage: CustomList<int> list1 = new CustomList<int>(); int i1 = 11; list1.add(i1); The.NET framework defines many generic interfaces useful for classes that define generic collections (see Figure 15-8, p. 477). 4

5 When we define a class that uses a generic type and an interface with generics, the interface has to be written with the generic type T: public class CustomerList<T> : IEnumerable<T> When we use an interface with a generic type, the actual type has to be specified : public class Customer : IGenericPersistable<Customer> 5

Classes. Logical method to organise data and functions in a same structure. Also known as abstract data type (ADT).

Classes. Logical method to organise data and functions in a same structure. Also known as abstract data type (ADT). UNITII Classes Logical method to organise data and functions in a same structure. Also known as abstract data type (ADT). It s a User Defined Data-type. The Data declared in a Class are called Data- Members