class、case class、object、case object的区别

opencode

发布于 2022-12-26 16:12:20

8640

发布于 2022-12-26 16:12:20

文章被收录于专栏：知识同步

scala记录

对于一般的class，是这样写的：

class Test1(var name: String, var age: Int){
    def method():Unit
    private var id
}

而对于case class，形式如下：

class Test2(name: String, age: Int)

case class的成员默认都是常量，所以case class适用于数据成员不改变的场景，而且case class之间可以进行比较

case class Message(sender: String, recipient: String, body: String)

val message2 = Message("jorge@catalonia.es", "guillaume@quebec.ca", "Com va?")
val message3 = Message("jorge@catalonia.es", "guillaume@quebec.ca", "Com va?")
val messagesAreTheSame = message2 == message3  // true

尽管message2和message3引用不同的对象，但是他们的值是相等的，所以message2 == message3为true。

case class也很适合做匹配，以下是做类型匹配：

abstract class Notification

case class Email(sender: String, title: String, body: String) extends Notification

case class SMS(caller: String, message: String) extends Notification

case class VoiceRecording(contactName: String, link: String) extends Notification

class Main{
    def showNotification(notification: Notification): String = {
    notification match {
        case Email(sender, title, _) =>
        s"You got an email from $sender with title: $title"
        case SMS(number, message) =>
        s"You got an SMS from $number! Message: $message"
        case VoiceRecording(name, link) =>
        s"you received a Voice Recording from $name! Click the link to hear it: $link"
    }
    }
}

一般的object，形式如下：

object Car{
    val numberOfWheels = 4

    def run(): Unit = {
        val currentDateAndTime: Date = new Date(System.currentTimeMillis())
        println(s"I am a new car running on $currentDateAndTime!")
    }
}

object对象是单例对象，和class不同的是，object是无参的，构造函数不能传入参数