Java，术语澄清 [英] Java, terminology clarification

问题描述

在Java中，对象可以有一个运行时类型（创建它的类型）和一个类型（你已经将它转换为的类型）。

In Java, an Object can have a runtime type (which is what it was created as) and a casted type (the type you have casted it to be).

我想知道这些类型的正确的名称是什么。例如

I'm wondering what are the proper name for these types. For instance

class A {

}

class B extends A {

}

A a = new B();

a创建为 B 但是它被声明为 A 。使用每个透视图引用 a 类型的正确方法是什么？

a was created as a B however it was declared as an A. What is the proper way of referring to the type of a using each perspective?

推荐答案

我认为区分对象（在执行时存在，只有其执行时间类型）和表达式（如变量）很重要）具有编译时类型。

I think it's important to distinguish between the object (which exists at execution time, and just has its execution time type) and an expression (such as a variable) which has a compile-time type.

所以在这种情况下：

A a = new B();

a 是一个类型为<的变量code> A 。它在执行时的值是对 B 类型的对象的引用。

a is a variable, of type A. Its value at execution time is a reference to an object of type B.

Java语言规范使用运行 -time class（例如，为了覆盖的目的，如在第15.12.4.4节）对象的类型。在其他地方我认为它只是使用type作为表达式的类型，这意味着编译时类型。

The Java language specification uses "run-time class" (e.g. for the purpose of overriding, as in section 15.12.4.4) for the type of an object. Elsewhere I think it just uses "type" for the type of an expression, meaning the compile-time type.

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