如何将java.util.List转换为Scala列表

Question

我有这个Scala方法,错误如下.无法转换为Scala列表.

 def findAllQuestion():List[Question]={
   questionDao.getAllQuestions()
 } 

类型不匹配; 发现:java.util.List[com.aitrich.learnware.model.domain.entity.Question]必填: scala.collection.immutable.List[com.aitrich.learnware.model.domain.entity.Question]

Answer 1

您可以使用Scala简单地转换List JavaConverters:

import scala.collection.JavaConverters._

def findAllQuestion():List[Question] = {
  questionDao.getAllQuestions().asScala
}

Answer 2

import scala.collection.JavaConversions._

会为你做隐式转换; 例如:

var list = new java.util.ArrayList[Int](1,2,3)
list.foreach{println}

Answer 3

def findAllStudentTest(): List[StudentTest] = { 
  studentTestDao.getAllStudentTests().asScala.toList
} 

Answer 4

开始Scala 2.13，该包scala.collection.JavaConverters被标记为已弃用，以支持scala.jdk.CollectionConverters：

import scala.jdk.CollectionConverters._

// val javaList: java.util.List[Int] = java.util.Arrays.asList(1, 2, 3)
javaList.asScala.toList
// List[Int] = List(1, 2, 3)

Answer 5

导入JavaConverters,@ fynn的响应丢失了toList

import scala.collection.JavaConverters._

def findAllQuestion():List[Question] = {
  //           java.util.List -> Buffer -> List
  questionDao.getAllQuestions().asScala.toList
}