超类方法与接口默认方法冲突解决 [英] Super class method and Interface default method conflict resolution

问题描述

考虑下面的例子，

public class Testing extends SupCls implements Intf {
    public static void main(String[] args) {
        new Testing().test();
    }
}

class SupCls {
    public void test() {
        System.out.println("From SupCls");
    }
}

interface Intf {
    public default void test() {
        System.out.println("From Intf");
    }
}

如您所见，SupCls 类和 Intf 接口之间没有联系.但两者都定义一种通用方法.

As you can see, there's no connection between SupCls class and Intf interface. But both are defining a common method.

和Testing 类正在扩展SupCls 并实现Intf.

And Testing class is extending SupCls and implementing Intf.

所以，当我在 Testing 上调用 test() 方法时，输出是，

So, when I call test() method on Testing the output is,

From SupCls

我认为这是有道理的，因为从类扩展应该比从接口实现具有更高的优先级.

Which I think makes sense because extending from a class should take higher priority than implementing from an interface.

但 eclipse 会报告其他情况，如下面的屏幕截图所示.

我坚信这是一个Eclipse 中的错误.

但在假设之前，此行为是否已定义&在 JLS 中记录?或者还有其他什么东西定义了这种行为?

But before assuming, is this behavior defined & documented in the JLS? Or is there something else which defines this behavior?

Eclipse 版本是 Mars Release (4.5.0)，如果重要的话.

Eclipse version is Mars Release (4.5.0), if it matters.

推荐答案

你的假设是对的，从超类继承的具体方法优先于interface中的default方法代码>:

Your assumption is right, the concrete method inherited from the superclass takes precedence over the default method from the interface:

JLS §8.4.8.继承、覆盖和隐藏

类C 从其直接超类和直接超接口继承所有抽象和默认(第9.4节)方法m 满足以下所有条件:

A class C inherits from its direct superclass and direct superinterfaces all abstract and default (§9.4) methods m for which all of the following are true:

…

• C 中声明的任何方法都没有作为 m 签名的子签名(第 8.4.2 节)的签名.
• C 从其直接超类继承的具体方法没有一个签名，该签名是 m 签名的子签名.

• No method declared in C has a signature that is a subsignature (§8.4.2) of the signature of m.
• No concrete method inherited by C from its direct superclass has a signature that is a subsignature of the signature of m.

引用的第二个要点在这里适用，有一个从具有适当签名的直接超类继承的具体方法，因此default 方法没有被继承.

The second cited bullet applies here, there is a concrete method inherited from the direct superclass with an appropriate signature, so the default method is not inherited.

文档甚至通过附加注释消除了任何疑问:

The documentation even clears any doubt with an additional remark:

请注意，继承的具体方法可能会阻止抽象或默认方法的继承.(稍后我们将断言具体方法覆盖来自 C"的抽象或默认方法.)

所以当涉及到 Testing 类时，它就像 SupCls.test() 覆盖了 Intf.test().

So it’s like SupCls.test() overrides Intf.test() when it comes to class Testing.

换句话说，你是对的，这是 Eclipse 中的一个错误，但只要它只影响提案的呈现方式，我就会认为它是一个小错误.插入的来源将是相同的，无论提案中是否已呈现 ^D.

In other words, you are right, it’s a bug in Eclipse, but as long as it only affects the way the proposal is rendered, I’d consider it a minor bug. The inserted source will be the same, regardless of whether a ^D has been rendered in the proposal or not.

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