如何在内部排列或链接枚举元素？ [英] How Enum elements are arranged or linked internally?

问题描述

在Java中，枚举是一种特殊类型的数据类型，通过查看数据类型字，我得到了几个问题，例如内存中是否有预定义的内存大小，或者是枚举设置为任何数据结构像队列用于快速访问

根据Java文档

枚举声明定义一个类（称为枚举类型）。枚举类体
可以包括方法和其他字段。编译器自动添加一些特殊的
方法，当它创建一个枚举。

为什么编译器为枚举添加特殊方法。有人可以点亮这个吗？

来源

提前感谢

解决方案

为什么编译器为枚举添加特殊方法。

基本上，您可以轻松获取枚举类型的值。

唯一额外的方法是 valueOf 和值。此外，还有一个用于每个类型的值的公共静态final 字段，以便您可以实际访问该类型的约束条件值。

想象一下，编译器没有添加 valueOf 和值方法（或至少值方法） - 你将如何访问枚举类型的所有值？这通常是一件有用的事情。

现在 EnumSet 提供了类似的功能，但是要获得所有值，您必须提供一个 class<> 引用，这可能是一个痛苦。 值方法稍微调用一点（尽管也可能更贵）。

请参阅 JLS第8.9节，详细的详细信息提供什么。

为了回答这些值的存储方式，指定每个值都有一个静态字段，执行细节，Oracle Java编译器还包括一个带有数组的静态字段，该数组基本上克隆在值方法中。

您可以自己看到：

 枚举Foo {
 BAR，BAZ ; 
} 
  

编译：

  javac Foo.java 
  

解码：

  javap -private Foo 
 
从Foo.java编译
 final class Foo extends java.lang。枚举<富> {
 public static final Foo BAR; 
 public static final Foo BAZ; 
 private static final Foo [] $ VALUES; 
 public static Foo [] values（）; 
 public static Foo valueOf（java.lang.String）; 
 private Foo（）; 
 static {}; 
} 
  

如果您使用 javap -c 你会看到 values（）基本上是：

  public static Foo [] values（）{
 return（Foo []）$ VALUES.clone（）; 
} 
  

静态初始化程序块创建有限的一组实例并设置字段。 / p>

In Java Enum is a special kind of datatype, by looking at the word datatype I got few questions like does it have predefined memory size in memory or Are the elements in Enum set to any data structure like Queue for fast access.

As per Java doc

The enum declaration defines a class (called an enum type). The enum class body can include methods and other fields. The compiler automatically adds some special methods when it creates an enum.

Why the compiler adds special methods to enum. Could anybody shed light on this?

Source

Thanks in advance?

解决方案

Why the compiler adds special methods to enum.

So that you can easily get at the values of the enum type, basically.

The only extra methods are valueOf and values. In addition, there are public static final fields, one for each value of the type - again, so that you can actually access the constrainted set of values of that type.

Imagine that the compiler didn't add valueOf and values methods (or at least the values method) - how would you access "all the values of the enum type"? It's often a useful thing to do.

Now EnumSet provides similar facilities, but to get "all the values" you have to provide a Class<> reference, which can be a pain. The values method is somewhat simpler to invoke (although potentially more expensive as well).

See the JLS section 8.9 for more details of exactly what's provided.

To answer the matter of how the values are stored, it's specified that there's a static field per value, but as an implementation detail the Oracle Java compiler also includes a static field with an array - that array is basically cloned in the values method.

You can see this for yourself:

enum Foo {
    BAR, BAZ;
}

Compile:

javac Foo.java

Decompile:

javap -private Foo

Compiled from "Foo.java"
final class Foo extends java.lang.Enum<Foo> {
  public static final Foo BAR;
  public static final Foo BAZ;
  private static final Foo[] $VALUES;
  public static Foo[] values();
  public static Foo valueOf(java.lang.String);
  private Foo();
  static {};
}

If you use javap -c you'll see that values() is basically:

public static Foo[] values() {
    return (Foo[]) $VALUES.clone();
}

The static initializer block creates the limited set of instances and sets the fields.

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