Since an enum constructor can only be invoked by its constants, why is it then allowed to be package-private?
问题:
回答1:
The constructor actually isn't package-private... it's implicitly private
the way interface methods are implicitly public
even if you don't add the keyword.
The relevant section of the JLS (§8.8.3) states:
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
public
orprotected
.
回答2:
It's a quirk of the language: enum constructors are implicitly private.
Interestingly, if you declare a package-visible enum constructor, like this:
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:
Cannot instantiate the type MyEnum