c# 第四课 interfaces

An interface is a contract(协定) that guarantees to a client how a class or struct will behave.

When a class implements an interface(实现一个接口), it tells any potential(可能的) client “I guarantee I’ll support all the methods, properties, events, and indexers of the named interface.”

These contracts are made manifest(表明) using the interface keyword, which declares a reference type(引用类型) that encapsulates(封装) the contract.

interface ICompressible
{
    void Compress();
    void Decompress();
}
interface ILoggedCompressible 
: ICompressible
{
    void LogSavedBytes();
}
public class Document : ILoggedCompressible 
{
    // 实现ICompressible
    public void Compress(){ …}
    public void Decompress() { …}
    // 实现ILoggedCompressible 
     public void LogSavedBytes() { …}
// 要实现所有的接口成员

as operator

foreach (Document doc in folder)
{
        IStorable isDoc = doc as IStorable;
        if (isDoc != null)
        {
                isDoc.Read();
        }else{
                Console.WriteLine("IStorable not supported");doc.Encrypt();
        }
…
}

as 有左右两个操作数
Casts the left operand to the type specified by the right operand.
Returns null if the cast fails.

Interface Vs. Abstract Class

Interfaces are very similar to abstract classes.

C# doesn’t allow multiple inheritance with classes.

C# does allow to implement any number of interfaces and derive from one base class.