如何将Scala高阶类型特征的混合类型与Java泛型类型匹配?

本文介绍了如何将Scala高阶类型特征的混合类型与Java泛型类型匹配?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我的项目是Java和Scala语言的混合体，但是会出现一些类型不匹配错误，我认为这是Java和Scala交流方面的常见问题. 我用简单的班级安排了舞台​​.环境是Java 1.8和Scala 2.11.7

my project is mixed java and scala language, but some type mismatch error occur and I think it's a common problem in term of java and scala communicate. I organized the stage with simple classes. Environment is java 1.8 and scala 2.11.7

class Item[+T](name: String) //ready use Item as MM type class Packet[+MM[_]] object GenS extends App { //use Item class def doWithPacket(packet: Packet[Item]) = {} //type error occur on packetFormJava variable form java val packetFormJava = GetGenJ.newPacketInJava doWithPacket(packetFormJava) //run well val packetFromScala = new Packet[Item] doWithPacket(packetFromScala) }

和简单的java类:

public class GetGenJ { public static Packet<Item> newPacketInJava() { return new Packet<Item>(); } }

遇到编译错误:

Error:(16, 16) type mismatch; found : Packet[Item[_]] required: Packet[Item] doWithPacket(packetFormJava) ^

任何帮助或建议谢谢.

推荐答案

换句话说，Java如何代表Scala的Packet [Item [_]]类型?

In other word, how does the java represent scala's Packet[Item[_]] type?

不是. Java根本没有更高类型的类型. MM种类较多的信息隐藏在@ScalaSignature内部.

It doesn't. Java simply doesn't have higher-kinded types. The information that MM is higher-kinded is hidden inside @ScalaSignature.

编写Packet<Item>时，您使用的是原始类型(因此，在Scala中代表)；您不能在newPacketInJava中使用Item<Something>.

When you write Packet<Item>, you are using a raw type (which, in turn, can't be represented in Scala); you couldn't use Item<Something> inside newPacketInJava.