通用方法调用的Java类型提示 [英] Java Type Hints on Generic Method Calling

问题描述

  public static< 
 
 ; T1，T2> Map< Map T1，Set< T2>>聚合（列表< Map< String，Object>>列表，字符串colK，字符串colV）
 {
 ... 
} 
  pre> 
 
 
由于某种原因，我很想这样称呼它 
 
 
  Map< String，Set< Integer>> map = aggregate< String，Integer>（lData，id，ref）; 
  
但它没有编译，除非我将它改为
 地图< String，Set< Integer>> map = aggregate（lData，id，ref）; 
  
我只是想知道为什么它不需要右侧的提示。而是给了我编译错误。它表示，在右边的提示之后，它预计会有一个分号。第二个是调用该方法的正确方法吗？请问有人能给我一些提示吗？
      正如所示这里，调用方法的方法是： 
 
 
  ClassName。< String，Integer> aggregate（lData，id，ref）; 
  
其中 ClassName 是类的名称该方法包含在。
 
I'm wondering what is the proper way to call a static method with a signature like this:
public static <T1, T2> Map<Map T1, Set<T2>> aggregate(List<Map<String, Object>> list, String colK, String colV)
{
    ...
}
I was tempted to call it like this for some reason
Map<String, Set<Integer>> map = aggregate<String, Integer>(lData, "id", "ref");
but it didn't compile unless I changed it to
Map<String, Set<Integer>> map = aggregate(lData, "id", "ref");
I'm just wondering why it didn't need the hints on the right hand side.  And instead gave me compilation error.  It says it expects a semi-colon after the hints on the right hand side.  Is the second one a proper way to call the method?  Could somebody shed me some light please?
解决方案
As shown here, the way to call the method would be:
ClassName.<String, Integer>aggregate(lData, "id", "ref");
where ClassName is the name of the class that the method is contained in.

                        
这篇关于通用方法调用的Java类型提示的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！