类和类型的区别 [英] Difference between class and type

问题描述

作为 Java 新手，我对 class 和 type 的概念感到困惑.例如，对象 "Hello World!" 应该属于 type String 还是 class String?或者两者都有?

Being new to Java, I'm confused between the concepts of class and type. For example, should the object "Hello World!" belong to the type String or class String? Or maybe both?

推荐答案

一个类就是一个类型.接口是一种类型.原语是一种类型.数组是一种类型.

A class is a type. An interface is a type. A primitive is a type. An array is a type.

因此，每个类型也是类(包括枚举常量)、接口、基元或数组.

Therefore, every type is also either a class (including an enum constant), an interface, a primitive, or an array.

有两种截然不同的类型:原始类型和引用类型:

There are two distinct categories of types: primitive types and reference types:

• 原始类型的变量总是保存相同类型的原始值.这样的值只能通过对该变量的赋值操作来更改.
• 引用类型的变量始终保存对对象的引用的值.所有对象，包括数组，都支持Object 类的方法.引用类型是类类型(包括枚举类型)、接口类型和数组类型.

• A variable of primitive type always holds a primitive value of that same type. Such a value can only be changed by assignment operations on that variable.
• A variable of reference type always holds the value of a reference to an object. All objects, including arrays, support the methods of class Object. The reference types are class types (including enum types), interface types, and array types.

每条数据都有一个类型，它定义了它的结构，即它占用了多少内存，它是如何布局的，更重要的是，你可以如何与之交互.

Every piece of data has a type which defines its structure, namely how much memory it takes up, how it is laid out, and more importantly, how you can interact with it.

原始类型示例:

1. int
2. 浮动
3. char
4. 布尔值

类类型示例:

1. String
2. Integer
3. Boolean
4. ArrayList
5. StringBuilder

接口类型示例:

1. 集合
2. List
3. 地图
4. 可序列化

数组类型示例:

1. int[]
2. String[]
3. 整数[][][]

基本上，任何可以称为变量的东西都有一个类型，而类是一种类型.

Basically, anything that you can refer to as a variable has a type, and classes are a kind of a type.

此处的更多信息:http://docs.oracle.com/javase/specs/jls/se8/html/jls-4.html

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