Scala 地图上的 Guava Maps.difference

Question

尝试执行以下操作，但得到 overloaded method value differences with alternatives: cannot be applied to java.util.Map[String, Any]


import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.google.common.collect.Maps

import scala.collection.JavaConverters._



object Testing extends App {

  val leftJson = """{
    "name": {
      "first": "John",
      "last": "Doe"
    },
    "address": null,
    "birthday": "1980-01-01",
    "company": "Acme",
    "occupation": "Software engineer",
    "phones": [
    {
      "number": "000000000",
      "type": "home"
    },
    {
      "number": "999999999",
      "type": "mobile"
    }
    ]
  }"""
  val rightJson = """{
    "name": {
      "first": "Jane",
      "last": "Doe",
      "nickname": "Jenny"
    },
    "birthday": "1990-01-01",
    "occupation": null,
    "phones": [
    {
      "number": "111111111",
      "type": "mobile"
    }
    ],
    "favorite": true,
    "groups": [
    "close-friends",
    "gym"
    ]
  }"""

  val mapper = new ObjectMapper
  mapper.registerModule(DefaultScalaModule)
  val leftMap = mapper.readValue(leftJson, classOf[Map[String, Any]])
  val rightMap = mapper.readValue(rightJson, classOf[Map[String, Any]])

  val differences = Maps.difference(leftMap.asJava, rightMap.asJava)

}

Error:(59, 26) overloaded method value difference with alternatives:
  [K, V](x: java.util.SortedMap[K, _ <: V], x: java.util.Map[_ <: K, _ <: V])com.google.common.collect.SortedMapDifference[K,V] <and>
  [K, V](x: java.util.Map[_ <: K, _ <: V], x: java.util.Map[_ <: K, _ <: V], x: com.google.common.base.Equivalence[_ >: V])com.google.common.collect.MapDifference[K,V] <and>
  [K, V](x: java.util.Map[_ <: K, _ <: V], x: java.util.Map[_ <: K, _ <: V])com.google.common.collect.MapDifference[K,V]
 cannot be applied to (java.util.Map[String,Object], java.util.Map[String,Object])
  val differences = Maps.difference(leftMap.asJava, rightMap.asJava)

Answer 1

好消息是您的代码可以使用 Scala 2.13.1 正确编译。

我也尝试使用 Scala 2.12.10 编译您的代码，确实出现了问题。

如果您向编译器提示类型参数，问题就会解决：

val differences = Maps.difference[String, Any](leftMap.asJava, rightMap.asJava)

Scala 地图上的 Guava Maps.difference

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