java - 该字段是模糊的，而它显然是隐藏的

Question

我知道并完全同意通过接口(interface)共享常量被视为 bad practice ，但我没有选择这个实现。随便:

interface SuperClassConstants {
    public static final String CONSTANT = "super";
}

interface SubClassConstants extends SuperClassConstants {
    public static final String CONSTANT = "sub";
}

class SuperClass implements SuperClassConstants {
}

class SubClass extends SuperClass implements SubClassConstants {
    public SubClass() {
        System.out.println(CONSTANT);
        // The field CONSTANT is ambiguous
    }
}

为什么模棱两可？常数不是隐藏的吗？我以为 Java 会理解我期待 “sub”...

Answer 1

根据 JLS 9.3 :

If two fields with the same name are inherited by an interface because, for example, two of its direct superinterfaces declare fields with that name, then a single ambiguous member results. Any use of this ambiguous member will result in a compile-time error.

SubClassConstants中的字段CONSTANT隐藏了SuperClassConstants的CONSTANT。但是 SubClass 类可以访问这两个 CONSTANT，因为它实际上实现了这两个接口(interface)。

您可以通过指定接口(interface)名称来消除歧义:

System.out.println(SubClassConstants.CONSTANT);

另请阅读 JLS 6.5.6.1 :

If an expression name consists of a single Identifier, then there must be exactly one declaration denoting either a local variable, parameter, or field visible (§6.4.1) at the point at which the Identifier occurs. Otherwise, a compile-time error occurs.