JAVA和C#执行HeadFirst装饰者模式的结果差异，求解？

JAVA版
//Beverage.java
public abstract class Beverage {
String description = "Unkown Beverage";

public String GetDescription(){
return description;
}

public abstract double Cost();
}
//CondimentDecorator.java
public abstract class CondimentDecorator extends Beverage {

public abstract String GetDescription();

}
//Espresso.java
public class Espresso extends Beverage {
public Espresso()
{
description = "Espresso";
}

public double Cost() {

return 1.99;
}

}
//HouseBlend .java
public class HouseBlend extends Beverage {

public double Cost() {
return .89;
}
public HouseBlend()
{
description = "House Blend Coffee";
}
}

//Mocha.java
public class Mocha extends CondimentDecorator {

Beverage beverage;
public Mocha(Beverage beverage)
{
this.beverage = beverage;
}

public String GetDescription() {

return beverage.GetDescription() + ", Mocha";
}

public double Cost() {

return .20 + beverage.Cost();
}

}

//main.java

public class Main {

/**

• @param args */ public static void main(String[] args) { Beverage bv = new Espresso(); System.out.println(bv.GetDescription() +" $"+bv.Cost());

Beverage bv2 = new HouseBlend();
bv2 = new Mocha(bv2);
System.out.println(bv2.GetDescription() +" $"+bv2.Cost());
}

}

运行结果
Espresso $1.99
House Blend Coffee, Mocha $1.09

##############################

C#版
//Beverage.cs
public abstract class Beverage
{
public string description = "Unkown Beverage";

public string GetDescription()
{
return description;
}

public abstract double Cost();
}

//CondimentDecorator.cs
public abstract class CondimentDecorator:Beverage
{
public abstract new string GetDescription();
}

//Espresso.cs
public class Espresso : Beverage
{
public Espresso()
{
description = "Espresso";
}
public override double Cost()
{
return 1.99;
}
}

//HouseBlend.cs
public class HouseBlend : Beverage
{
public HouseBlend()
{
description = "House Blend Coffee";
}
public override double Cost()
{
return .89;

}
}

//Mocha.cs
public class Mocha : CondimentDecorator
{
Beverage beverage;
public Mocha(Beverage beverage)
{
this.beverage = beverage;
}

public override double Cost()
{
return .20 + beverage.Cost();
}

public override string GetDescription()
{
return beverage.GetDescription() + ", Mocha";
}
}

Program.cs
class Program
{
static void Main(string[] args)
{
Beverage bv = new Espresso();
Console.WriteLine(bv.GetDescription() + " $"+bv.Cost());

Beverage bv2 = new HouseBlend();

bv2 = new Mocha(bv2);

Console.WriteLine(bv2.GetDescription() + " $" + bv2.Cost());
Console.ReadKey();
}
}
运行结果：
Espresso $1.99
Unkown Beverage $1.09

public abstract new string GetDescription();
->
public abstract string GetDescription();