Java枚举和具有私有构造函数的类之间有什么区别？ [英] What are the differences between a Java enum and a class with private constructor?

问题描述

我正在尝试了解Java枚举是如何工作的，而且我得出的结论与一个普通的Java类非常相似，它将其构造函数声明为private。

I was trying to understand how Java enum really works and I have come to the conclusion that is very similar to a normal Java class that has it's constructor declared private.

我刚刚得出这个结论，它不是基于很多思考，而是想知道我是否想念任何东西。

I have just come to this conclusion and it isn't based on much thinking, but Id like to know whether I miss anything.

所以下面是一个简单的Java枚举和等效的Java类。

So below is an implementation of a simple Java enum and an equivalent Java class.

public enum Direction {
    ENUM_UP(0, -1),
    ENUM_DOWN(0, 1),
    ENUM_RIGHT(1, 0),
    ENUM_LEFT(-1, 0);


    private int x;
    private int y;

    private Direction(int x, int y){
        this.x = x;
        this.y = y;
    }
    public int getEnumX(){
        return x;
    }
    public int getEnumY(){
        return y;
    }
}

上面的代码和下面？

public class Direction{
    public static final Direction UP = new Direction(0, -1) ;
    public static final Direction DOWN = new Direction(0, 1) ;
    public static final Direction LEFT = new Direction(-1, 0) ;
    public static final Direction RIGHT = new Direction(1, 0) ;


    private int x ;
    private int y ;

    private Direction(int x, int y){
        this.x = x ;
        this.y = y ;
    }
    public int getX(){
        return x;
    }
    public int getY(){
        return y;
    }
}

推荐答案

差异：

1. 枚举扩展 java.lang.Enum 并获得所有好的功能：
   

1. Enums extend java.lang.Enum and gain all of its nice features:

1. 通过正确的序列化自动单例行为


2. 枚举值自动可读的 .toString 方法，而不需要复制您的枚举名称


3. .name 和 .ordinal 专用方法


4. 可用于基于高性能位元的 EnumSet 和 EnumMap classes

1. Automatic singleton behaviour through correct serialization
2. Automatic human-readable .toString method on enum values without the need to duplicate your enum names
3. .name and .ordinal special-purpose methods
4. Usable in high-performance bitset-based EnumSet and EnumMap classes

枚举由语言特别处理：

Enums are treated by the language specially:

1. 枚举使用一种特殊语法，可简化实例创建，而无需书写几十个 public static final fields


2. 枚举可用于 switch 语句


3. 枚举不能插入枚举列表之外，除了使用反射之外，还包含


4. 枚举不能在枚举列表之外扩展

1. Enums use a special syntax which simplifies instance creation without writing dozens of public static final fields
2. Enums can be used in switch statements
3. Enums cannot be instantiated outside the enumeration list except by using reflection
4. Enums cannot be extended outside the enumeration list

Java自动编译枚举中的额外内容：

Java automatically compiles extra stuff into enums:

1. public static（Enum）[] values（）;


2. public static（Enum）valueOf（java.lang.String）;


3. private static final（Enum）[] $ VALUES; （ values（）返回一个克隆）

1. public static (Enum)[] values();
2. public static (Enum) valueOf(java.lang.String);
3. private static final (Enum)[] $VALUES; (values() returns a clone of this)

大多数可以使用适当设计的类模拟，但枚举只是使用这套特别理想的属性创建一个类非常简单。

Most of these can be emulated with a suitably designed class, but Enum just makes it really easy to create a class with this set of particularly desirable properties.

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