1.官方Feature

213: Milling Project Coin

Support for private methods in interfaces was briefly in consideration for inclusion in Java SE 8 as part of the effort to add support for Lambda Expressions, but was withdrawn to enable better focus on higher priority tasks for Java SE 8. It is now proposed that support for private interface methods be undertaken thereby enabling non abstract methods of an interface to share code between them.

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2.使用说明

Java 8中规定接口中的方法除了抽象方法之外，还可以定义静态方法和默认的方法。一定程度上，扩展了接口的功能，此时的接口更像是一个抽象类。

在Java 9中，接口更加的灵活和强大，连方法的访问权限修饰符都可以声明为private的了，此时方法将不会成为你对外暴露的API的一部分。

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3.使用举例