点运算符“。”（通用参数之前）是什么意思？ [英] What does the dot operator `.` (before the generic parameter) mean?

问题描述

我今天看到这段代码：

  ImmutableMap< Class< ;?扩展ClientCommand>，CommandProcessorInterface> immutableMap = 
 ImmutableMap。< Class< ;?扩展ClientCommand>，CommandProcessorInterface>（... 
  

这个语法是什么意思？

ImmutableMap。< Class ..

我知道泛型是

有什么区别：

ImmutableMap< Class .. and ImmutableMap。< Class ..

解决它意味着你在 ImmutableMap 中调用一个通用静态方法，称为 类。

这与调用静态方法几乎相同，该方法嵌套在某个类中：

  SomeClass.staticMethod（）; 
  

对于您的方法定义了类型参数的情况，您可以明确地提供泛型类型，并且这样做是这样的：

<$ p < Type> genericStaticMethod（）;

最后回答你的问题：

ImmutableMap< ; Class ...> 和 ImmutableMap。< Class ... ？

第一个通常用于创建泛型类的实例。它用于在类级别上定义泛型，而第二个用于调用嵌套在某个类中的泛型静态方法。

I saw this code today:

    ImmutableMap<Class<? extends ClientCommand>, CommandProcessorInterface> immutableMap =
            ImmutableMap.<Class<? extends  ClientCommand>, CommandProcessorInterface>of(...

What does this syntax mean?

ImmutableMap.<Class ..

I knew generics was right after the class name. No?

What is the difference between:

ImmutableMap<Class.. and ImmutableMap.<Class..

解决方案

It means you're invoking a generic static method, called of in the ImmutableMap class.

It's pretty much the same as you're invoking a static method, nested in some class:

SomeClass.staticMethod();

For the cases when your method has a type-parameter defined, you can explicitly provide the generic type and this is done like this:

SomeClass.<Type>genericStaticMethod();

And to answer you final question:

What is the difference between ImmutableMap<Class...> and ImmutableMap.<Class... ?

The first is usually used when creating an instance of a generic class. It's used to define the generic-type on class level, while the second is used to invoke a generic static method that's nested in some class.

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