无法静态引用非静态字段memberVariable与private变量 [英] Cannot make a static reference to the non-static field memberVariable with private variable

问题描述

我用一个私有成员变量创建了一个枚举。
当我尝试访问成员变量时，编译状态为无法静态引用非静态字段memberVariable。

I created a enum with one private member variable. When i try to access the member variable the compiles states 'Cannot make a static reference to the non-static field memberVariable'.

如果该变量不是私有变量（例如，受保护或受包保护），则可以正常编译。我不了解变量的范围与实现的抽象函数的类型（静态，非静态）有什么关系。

If the variable is not private (e.g. protected or package protected) it compiles fine. I don't understand what the scope of the variable has to do with the type (static, non static) of the implemented abstract function.

有人能启发我吗？

public enum EnumWithAbstractMethodAndMembers {
    TheOneAndOnly(1) {
        @Override
        public int addValue(final int value) {
            return memberVariable + value;
        }
    };

    private final int memberVariable;

    private EnumWithAbstractMethodAndMembers(final int memberVariable) {
        this.memberVariable = memberVariable;
    }

    abstract int addValue(int value);

}

推荐答案

错误消息令人困惑。

问题是当您提供枚举值代码时，您正在创建枚举的匿名子类。 （其类为 EnumWithAbstractMethodAndMembers $ 1 ）子类无法访问其超类的私有成员，但是嵌套类可以通过生成的访问器方法访问。您应该能够访问私有字段，并且它给您的错误消息似乎具有误导性。

The problem is that when you give an enum value code, you are creating an anonymous sub class of the enum. (Its class will be EnumWithAbstractMethodAndMembers$1) A sub-class cannot access the private members of its super-class, however nested classes can via generated accessor method. You should be able to access the private field, and the error message it gives you appears to be mis-leading.

BTW您可以使用此功能，但不能这样做

BTW You can use this, but you shouldn't need to IMHO.

    public int addValue(final int value) {
        return super.memberVariable + value;
    }

---

这里是一个较短的例子我将在错误消息中记录为错误，因为它不会导致问题的解决。

---

Here is a shorter example I will log as a bug in the error message as it doesn't lead to a solution to the problem.

public enum MyEnum {
    One {
        public int getMemberVariableFailes() {
            // error: non-static variable memberVariable cannot be referenced from a static context
            return memberVariable;
        }

        public int getMemberVariable2OK() {
            return memberVariable2;
        }

        public int getMemberVariableOK() {
            return super.memberVariable;
        }
    };

    private final int memberVariable = 1;
    final int memberVariable2 = 1;
}

---

根据汤姆·霍金（Tom Hawkin）的反馈，此示例将获得相同的错误消息。

---

Based on Tom Hawkin's feedback, this example gets the same error message.

public class MyNotEnum {
    // this is the static context in which the anonymous is created
    public static final MyNotEnum One = new MyNotEnum() {
        public int getMemberVariableFailes() {
            // error: non-static variable memberVariable cannot be referenced from a static context
            return memberVariable;
        }

        public int getMemberVariableOK() {
            return super.memberVariable;
        }
    };
    private final int memberVariable = 1;
}

进行比较

public class MyNotEnum {
    public class NestedNotEnum extends MyNotEnum {
        public int getMemberVariableFailes() {
            // compiles just fine.
            return memberVariable;
        }

        public int getMemberVariableOK() {
            return super.memberVariable;
        }
    }
    private final int memberVariable = 1;
}

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