Java:与 new 关键字的接口怎么可能? [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，在这里我很困惑；

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

这段代码来自 jaxb 库中的 Document.java，ContentVisitor 是一个 Interface 在同一个包中，我们如何创建一个带有 new 关键字的 Interface 实例?这不违法吗?

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

在代码中，您没有创建接口的实例.相反，代码定义了一个匿名类来实现接口，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();
}

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