type information - Generic Class References_typeinformation:generictype-优快云博客

本文链接：https://blog.youkuaiyun.com/wangbingfengf98/article/details/96777508

本文探讨了Java中Class引用的使用方式及其与泛型结合的可能性。通过具体示例展示了如何利用泛型来约束Class引用的目标类型，并解释了这种类型约束如何帮助开发者减少类型错误。

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A Class reference points to a Class object, which manufactures instances of classes and contains all the method code for those instances. It also contains the statics for that class. So a Class reference really does indicate the exact type of what it’s pointing to: an object of the class Class.

However, the Java designers saw an opportunity to make this a bit more specific by allowing we to constrain the type of Class object to which the Class reference points, using the generic syntax. In the following example, both syntaxes are correct:

// typeinfo/GenericClassReferences.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

public class GenericClassReferences {
  public static void main(String[] args) {
    Class intClass = int.class;
    // generic syntax allows the compiler to enforce extra type checking.
    Class<Integer> genericIntClass = int.class;
    genericIntClass = Integer.class; // Same thing
    intClass = double.class;
    // genericIntClass = double.class; // [1] Illegal
  }
}

When uncomment [1], it prompts bellow error

typeinfo/GenericClassReferences.java:12: error: incompatible types: Class<Double> cannot be converted to Class<Integer
>
    genericIntClass = double.class; // [1] Illegal
                            ^
1 error

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/typeinfo/GenericClassReferences.java