为什么我不能初始化一个Map< int，String>？

我想存储一组 int / String 值，但 int 不一定是增量的，这意味着数据可以是：

I want to store a set of int/String values, but the ints are not necessarily incremental, meaning the data can be:

<1, "first">, <3, "second">, <9, "third">. 

所以我试图创建一个c＃等价的一个 Dictionary< int ，字符串> ，但它只是无法编译，表示语法错误在令牌上int，这个标记之后的尺寸在行上：

So I'm trying to create the c# equivalent of a Dictionary<int, string> but it just fails to compile, saying "Syntax error on token "int", Dimensions expected after this token" on the line:

private Map<int, String> courses;

有人可以告诉我为什么会这样吗？还有一个很好的替代方法是将对象创建为 int 和 String 的占位符，然后使用数组来存储它们

Can anyone please tell me why this is? And a good alternative to creating an object as a placeholder for the int and String, then using an array to store them?