从父类函数覆盖类变量 [英] Override a class variable from parent classes function

问题描述

我有一个父母和孩子班.

I have a parent and child class.

class a {
val name :String = "jo"
 def extract(){
  println(name)
 }
}

现在我需要执行以下操作.

now i need to do as below.

class b extends a {
 override def extract(){
  override var name :String = "dave". //the problem is here and
  super.extract()
  name = "jenny" //here
  super.extract()
 }
}

现在让我面对.

1)如果im要覆盖类a中的值，并且需要不可变才能使用覆盖，则不能使用var.

1) I cannot use var if im to override the value in class a, needs to be immutable to use override.

2)需要使用不同的变量调用两次超级函数.

2) needs to call the super function twice with different variable.

3)无法在函数内部调用覆盖

3) Cannot call override inside the function

如果有人知道如何解决这个问题，我将非常感谢.我不能在A类课上做任何改变.我只能在b上工作，并且需要使用不同的变量值调用两次extract函数.

Would really appreciate if anyone knew how to get around this. I cannot change anything in class a. I can work only on b and needs to call the extract function twice with different values for the variable.

推荐答案

无法在方法中覆盖超类不可变值.

It's not possible to override super class immutable values inside method.

相反，您可以在超级类中更改var，但不能在子类中覆盖.

Instead you can change var in super class but don't override in child class.

请检查以下代码.

scala> :paste
// Entering paste mode (ctrl-D to finish)

class a {
 var name = ""
 def extract(){
  println(name)
 }
}


class b extends a {
 override def extract(){
  name = "dave" //the problem is here and
  super.extract()
  name = "jenny" //here
  super.extract()
 }
}

// Exiting paste mode, now interpreting.

defined class a
defined class b

scala> (new b).extract
dave
jenny

如果要使用不同的name值两次调用extract方法，只需扩展父类&覆盖名称，创建具有不同名称值的子对象，如下所示.

If you want to call extract method twice with different name values, Just extend parent class & override name, create child object with different name values like below.

scala> :paste
// Entering paste mode (ctrl-D to finish)

class a {
 val name = ""
 def extract(){
  println(name)
 }
}


class b (override val name: String) extends a {
 override def extract(){
  super.extract()
 }
}

// Exiting paste mode, now interpreting.

defined class a
defined class b

scala> (new b("dave")).extract
dave

scala> (new b("jenny")).extract
jenny

scala>

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