java 为什么枚举可以有一个包私有构造函数？
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Why can a enum have a package-private constructor?
提问by Tobias
Since an enum constructor can only be invoked by its constants, why is it then allowed to be package-private?
既然枚举构造函数只能由它的常量调用，那么为什么允许它是包私有的呢？
回答by ColinD
The constructor actually isn't package-private... it's implicitly privatethe way interface methods are implicitly publiceven if you don't add the keyword.
构造函数实际上不是包私有的......即使您不添加关键字，它也是隐式private接口方法的隐式方式public。
The relevant section of the JLS (§8.8.3) states:
JLS ( §8.8.3)的相关部分指出：
If no access modifier is specified for the constructor of a normal class, the constructor has default access.
If no access modifier is specified for the constructor of an enum type, the constructor is
private.It is a compile-time error if the constructor of an enum type (§8.9) is declared
publicorprotected.
如果没有为普通类的构造函数指定访问修饰符，则构造函数具有默认访问权限。
如果没有为枚举类型的构造函数指定访问修饰符，则构造函数为
private。如果声明了枚举类型（第 8.9 节）的构造函数
public或protected.
回答by Bohemian
It's a quirk of the language: enum constructors are implicitly private.
这是该语言的一个怪癖：枚举构造函数是隐式私有的。
Interestingly, if you declare a package-visible enum constructor, like this:
有趣的是，如果你声明一个包可见的枚举构造函数，像这样：
public enum MyEnum {
A(0),
B(1);
private final int i;
MyEnum(int i) {
this.i = i;
}
public int getI() {
return i;
}
}
you can't refer to it from another class in the package. If you try, you get the compiler error:
你不能从包中的另一个类引用它。如果你尝试，你会得到编译器错误：
Cannot instantiate the type MyEnum
无法实例化 MyEnum 类型
