为什么 Java 的 Class<T> 是泛型的？
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Why is Java's Class<T> generic?
提问by ripper234
Why is Java's Class<T>generic?
为什么Java是Class<T>泛型的？
采纳答案by Steve B.
So that generic typed methods can be used -
以便可以使用泛型类型方法 -
Class<Foo> klass = Foo.class;
Foo f = klass.newInstance();
Foo f = klass.cast(Object);
回答by Chris Arguin
Here is a reasonably good summary of the advantages: http://download.oracle.com/javase/tutorial/extra/generics/literals.html
以下是对优点的合理总结：http: //download.oracle.com/javase/tutorial/extra/generics/literals.html
回答by Bill the Lizard
There's a short mention of this in the Genericssection of the 1.5 version of the language guide:
在 1.5 版语言指南的泛型部分中简短地提到了这一点：
More surprisingly, class Class has been generified. Class literals now function as type tokens, providing both run-time and compile-time type information. This enables a style of static factories exemplified by the getAnnotation method in the new AnnotatedElement interface:
更令人惊讶的是，Class Class 已经被泛型化了。类文字现在用作类型标记，提供运行时和编译时类型信息。这启用了一种静态工厂样式，例如新 AnnotatedElement 接口中的 getAnnotation 方法：
<T extends Annotation> T getAnnotation(Class<T> annotationType);
This is a generic method. It infers the value of its type parameter T from its argument, and returns an appropriate instance of T, as illustrated by the following snippet:
这是一个通用的方法。它从其参数推断其类型参数 T 的值，并返回 T 的适当实例，如以下代码段所示：
Author a = Othello.class.getAnnotation(Author.class);
Prior to generics, you would have had to cast the result to Author. Also you would have had no way to make the compiler check that the actual parameter represented a subclass of Annotation
在使用泛型之前，您必须将结果强制转换为 Author。此外，您将无法让编译器检查实际参数是否代表 Annotation 的子类
回答by Jér?me Verstrynge
The real reason is given by Neil Gafter:
真正的原因是Neil Gafter给出的：
When we added generics to Java in JDK5, I changed the class java.lang.Class to become a generic type. For example, the type of String.class is now Class < String > . Gilad Bracha coined the term type tokens for this. My intent was to enable a particular style of API, which Joshua Bloch calls the THC, or Typesafe Heterogenous Container pattern.
当我们在JDK5中为Java添加泛型时，我将类java.lang.Class更改为泛型类型。例如， String.class 的类型现在是 Class < String > 。Gilad Bracha 为此创造了术语类型标记。我的意图是启用一种特定风格的 API，Joshua Bloch 将其称为 THC，或 Typesafe Heterogenous Container 模式。
