Java：与新关键字的接口如何可能？ [英] Java: Interface with new keyword how is that possible?

问题描述

我正在从Java库中读取一些源代码，我在这里感到困惑;

I was reading some sourcecode from Java libraries, and I am confused here;

此代码来自jaxb库中的Document.java， ContentVisitor是一个接口在同一个包中，我们如何用一个新关键字创建一个Interface实例？是不是非法？

This code is from Document.java in jaxb library, and ContentVisitor is an Interface in same package, how can we create an instance of Interface with a new keyword? isn't that illegal?

public final class Document {
.
.
 private final ContentVisitor visitor = new ContentVisitor() {
    public void onStartDocument() {

        throw new IllegalStateException();
    }

    public void onEndDocument() {
        out.endDocument();
    }

    public void onEndTag() {
        out.endTag();
        inscopeNamespace.popContext();
        activeNamespaces = null;
    }
}

推荐答案

In代码，你不是在创建一个接口实例。相反，代码定义了一个实现接口的匿名类，并实例化该类。

In the code, you're not creating an instance of the interface. Rather, the code defines an anonymous class that implements the interface, and instantiates that class.

代码大致相当于：

public final class Document {

    private final class AnonymousContentVisitor implements ContentVisitor {

        public void onStartDocument() {
            throw new IllegalStateException();
        }

        public void onEndDocument() {
            out.endDocument();
        }

        public void onEndTag() {
            out.endTag();
            inscopeNamespace.popContext();
            activeNamespaces = null;
        }
    }

    private final ContentVisitor visitor = new AnonymousContentVisitor();
}

这篇关于Java：与新关键字的接口如何可能？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！