为什么 scala 伴随对象的 apply() 返回 Unit

Question

我正在学习 Scala。

class Student(var name:String, var age:Int) {
    private var sex:Int = 0
    println("class method")

    def apply() = {
       println("class apply method")
    }
}

object Student {
  def apply(name:String, age:Int): Unit = {
    println("object apply")
    new Student(name, age)
  }
  def main(args: Array[String]): Unit = {
    val student = Student("john", 29)
  }
}

main 中的Student("john", 29) 应该给出Student，但它返回Unit。

任何解释都会有所帮助。谢谢！

Answer 1

您已通过显式声明自己的 Student 伴随对象来覆盖编译器生成的默认 Student 伴随对象的行为

object Student {
  def apply(name:String, age:Int): Unit = { //Here is the problem. Return type is Unit instead of Student
    println("object apply")
    new Student(name, age)
  }
  def main(args: Array[String]): Unit = {
    val student = Student("john", 29)
  }
}

把你的代码改成下面的代码 sn -p

object Student {
  def apply(name:String, age:Int): Student = { //Changed the return type to Student
    println("object apply")
    new Student(name, age)
  }
  def main(args: Array[String]): Unit = {
    val student = Student("john", 29)
  }
}