C# 抽象类

public abstract class Item { 
    // Note empty implementation 
    public abstract decimal NetValue { get; } 
} 

public class Product : Item { 
    public long InStoreCount; 
    public decimal CurrentPrice;
    // Override like a virtual method. 
    public override decimal NetValue {
       get { 
          return CurrentPrice * InStoreCount; 
       } 
    } 
}