关于继承：无法在scala中覆盖子类的方法

Unable to override a method from child class in scala

我在自学斯卡拉。我试图实现继承，却偶然发现了一个小问题。有人能帮我吗？

问题：

在下面的代码中，为什么我不能为对象p6、p7和p8设置x的值。

为什么我无法覆盖我的孩子类中的def setx？

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object classes {
def main (args: Array[String]) {
//create objects for class Point
val p1 = new Point
println("P1 created using no argument constructor:"+p1.toString())

val p2 = new Point
p2.setX(1)
println("P2 created using setter methods:"+p2.toString())

val p3 = new Point(2)
println("P3 created using single argument constructor:"+p3.toString())

val p4 = new Point(3,1)
//demonstrating how to use objects within println statement
println(s"P4 is created using default constructor and its x value is ${p4.getX} its y value is ${p4.getY} and its id is ${p4.id}")

val p5 = new ThreeD
println("P5 is created using no argument constructor of 3D class:"+p5.toString)

val p6 = new ThreeD(2)
println("P6 is created using single argument constructor of 3D class:"+p6.toString)

val p7 = new ThreeD(2,3)
println("P7 is created using two argument constructor of 3D class:"+p7.toString)

val p8 = new ThreeD(2,3,4)
p8.setX(5) // has no effect.. why??
println("P8 is created using default constructor of 3D class:"+p8.toString)
}

//The class name works as a class constructor which can take a number of parameters.
class Point (var x: Int, var y: Int) {
//demonstrating how to protect the values
this.setX(x)

/*
Scala does not have static methods or static variables.
However we can mimic its behavior.

Outside the scope of the class, create a companion object for the class
Companion objects has same name as that of the class and holds the static members and functions.
*/

val id = Point.getId

//lets define getters and setters
def getX() : Int = x
def getY() : Int = y

def setX(x: Int) {
this.x = x
}

//this is how we override a function
//here we implement our custom toString() method
override def toString() : String = {
return"(%d, %d) and id is %d".format(this.x, this.y, this.id)
}

//lets define other constructors

//to define a constructor, we create a method called"this"
//constructor with no arguments
def this () {
this(0,0)
}

//constructor with 1 value
def this (x: Int) {
this(0,0)
this.setX(x)
}

}

object Point {
//static member
private var id = 0

//static method
private def getId () : Int = { id += 1; id}
}

//Inheritance
class ThreeD (x: Int, y: Int, z: Int) extends Point (x, y) {
def this(x: Int, y: Int) {
this(0,y,0)
this.setX(x)
}

def this(x: Int) {
this(0,0,0)
this.setX(x)
}

def this() {
this(0,0,0)
}

//to override parent class's setX method
override def setX(x: Int) {
super.setX(x)
}

override def toString() : String = {
return"(%d, %d, %d) and id is %d".format(this.x, this.y, this.z, this.id)
}
}
}