什么是类?在 Java 中是什么意思? [英] What does Class<?> mean in Java?

问题描述

我的问题如上所述.抱歉，这可能是重复的，但我找不到结尾带有 <?> 的示例.

My question is as above. Sorry, it's probably a duplicate but I couldn't find an example with the <?> on the end.

为什么不直接使用 Class 作为参数?

Why would you not just use Class as the parameter?

推荐答案

Class 是一个可参数化的类，因此你可以使用语法 Class where T 是一种类型.通过编写 Class，您声明了一个 Class 对象，该对象可以是任何类型(? 是通配符).Class 类型是一种包含有关类的元信息的类型.

Class is a parameterizable class, hence you can use the syntax Class<T> where T is a type. By writing Class<?>, you're declaring a Class object which can be of any type (? is a wildcard). The Class type is a type that contains meta-information about a class.

通过指定泛型类型的特定类型来引用泛型总是好的做法，通过使用 Class 你尊重这种做法(你知道 Class 是可参数化的)但您并没有限制您的参数具有特定类型.

It's always good practice to refer to a generic type by specifying his specific type, by using Class<?> you're respecting this practice (you're aware of Class to be parameterizable) but you're not restricting your parameter to have a specific type.

关于泛型和通配符的参考:http://docs.oracle.com/javase/tutorial/java/generics/wildcards.html

Reference about Generics and Wildcards: http://docs.oracle.com/javase/tutorial/java/generics/wildcards.html

关于Class对象和反射(Java语言用来自省的特性)的参考:https://www.oracle.com/technetwork/articles/java/javareflection-1536171.html

Reference about Class object and reflection (the feature of Java language used to introspect itself): https://www.oracle.com/technetwork/articles/java/javareflection-1536171.html

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