@FunctionalInterfaces可以有默认方法吗？ [英] Can @FunctionalInterfaces have default methods?

问题描述

为什么我不能使用默认方法实现创建 @FunctionalInterface ？

Why can't I create a @FunctionalInterface with a default method implementation?

@FunctionalInterface
public MyInterface {
    default boolean authorize(String value) {
        return true;
    }
}

推荐答案

你可以在功能界面中使用默认方法，但其合同要求您提供一种抽象方法（或SAM）。由于默认方法具有实现，因此它不是抽象的。

You can have default methods in a functional interface but its contract requires you to provide one single abstract method (or SAM). Since a default method have an implementation, it's not abstract.

从概念上讲，功能接口只有一个抽象方法。
由于默认方法有实现，因此它们不是抽象的。

Conceptually, a functional interface has exactly one abstract method. Since default methods have an implementation, they are not abstract.

和

如果使用此注释类型注释类型，则生成错误消息所需的编译器为
，除非：

If a type is annotated with this annotation type, compilers are required to generate an error message unless:

类型是接口类型，而不是注释类型，枚举或
类。

The type is an interface type and not an annotation type, enum, or class.

带注释的类型满足功能性
接口的要求。

The annotated type satisfies the requirements of a functional interface.

这里您不满足功能接口的要求，因此您需要提供一种抽象方法。例如：

Here you don't satisfy the functional interface's requirement, so you need to provide one abstract method. For example:

@FunctionalInterface
interface MyInterface {

    boolean authorize(int val);

    default boolean authorize(String value) {
        return true;
    }
}

请注意，如果您声明一个覆盖其中一个的抽象方法一个来自Object类的公共方法，它不计算，因为这个接口的任何实现都将至少通过Object的类来实现这些方法。例如：

Note that if you declare an abstract method overriding one of a public method from the Object's class it doesn't count, because any implementation of this interface will have an implementation of those methods through at least the Object's class. For example:

@FunctionalInterface
interface MyInterface {

    default boolean authorize(String value) {
        return true;
    }

    boolean equals(Object o);
}

无法编译。

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