Kotlin嵌套类可见性与实例控制：实现父类专属创建与外部受限访问

class Sphere(val radius: Double = 1.toDouble()) {      // 编译错误：'public' property exposes its 'private-in-class' type argument Point     var pointsLinkedHashSet: LinkedHashSet<Point> = linkedSetOf()      // 编译错误：'public' function exposes its 'private-in-class' return type argument Point     fun getPoints(): LinkedHashSet<Point> {         return pointsLinkedHashSet     }      fun addPoint(latitude: Double, longitude: Double): Point {         val point = Point(this.radius, latitude, longitude)         pointsLinkedHashSet.add(point)         return point     }      private class Point( // private class         val radius: Double,         val latitude: Double,         val longitude: Double     ) }

// Java 示例 public class Sphere {     private final Double radius;     private final LinkedHashSet<Point> pointsLinkedHashSet = new LinkedHashSet<>();      public Sphere(Double radius) {         this.radius = radius;     }      public Point addPoint(Double latitude, Double longitude) {         Point point = new Point(latitude, longitude); // 外部类可以调用私有构造函数         pointsLinkedHashSet.add(point);         return point;     }      // 非静态内部类，默认可访问外部类成员     class Point {         private final Double radius;         private final Double latitude;         private final Double longitude;          // 私有构造函数，外部无法直接创建 Point 实例         private Point(Double latitude, Double longitude) {             this.radius = Sphere.this.radius; // 访问外部类的 radius             this.latitude = latitude;             this.longitude = longitude;         }          // 公共 getter 方法         public Double getRadius() { return radius; }         public Double getLatitude() { return latitude; }         public Double getLongitude() { return longitude; }     } }  // Java 外部调用示例 public class Main {     public static void main(String[] args) {         Sphere sphere = new Sphere(1.0);         Sphere.Point point = sphere.addPoint(10.0, 20.0); // 可以获取 Point 实例         System.out.println(point.getLatitude()); // 可以访问 Point 属性          // Sphere.Point newPoint = new Sphere.Point(30.0, 40.0); // 编译错误：构造函数私有     } }

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class Sphere(val radius: Double = 1.toDouble()) {      val pointsLinkedHashSet: LinkedHashSet<Point> = linkedSetOf()      fun getPoints(): LinkedHashSet<Point> {         return pointsLinkedHashSet     }      fun getLastPoint(): Point? = pointsLinkedHashSet.lastOrNull()      fun clearPoints() = pointsLinkedHashSet.clear()      fun addPoint(latitude: Double, longitude: Double): Point {         // Sphere 内部可以调用 Point 的私有构造函数         val point = Point(latitude, longitude)         pointsLinkedHashSet.add(point)         return point     }      // Point 必须是 public (默认) 才能被 public 函数返回     inner class Point private constructor( // 私有构造函数         val latitude: Double,         val longitude: Double     ) {         // Point 实例可以访问外部类的 radius         val radius: Double = this@Sphere.radius          override fun toString(): String {             return "Point(radius=$radius, latitude=$latitude, longitude=$longitude)"         }     } }  // 外部调用示例 fun main() {     val sphere = Sphere(1.0)     println("Sphere radius = ${sphere.radius}")      // 外部可以通过 Sphere 方法获取 Point 实例     val point = sphere.addPoint(10.0, 20.0)     println("Point: $point")     println("Point radius = ${point.radius}")     println("Point latitude = ${point.latitude}")      val point1 = sphere.getLastPoint()     println("Point1: $point1")      // 编译错误：Cannot access '<init>': it is private in 'Point'     // val newPoint = Sphere.Point(30.0, 40.0)      // 编译错误：Cannot access '<init>': it is private in 'Point'     // val newPointFromInstance = sphere.Point(30.0, 40.0) }

interface IPoint {     val radius: Double     val latitude: Double     val longitude: Double }  class Sphere(val radius: Double = 1.toDouble()) {      private val pointsLinkedHashSet: LinkedHashSet<Point> = linkedSetOf()      fun getPoints(): LinkedHashSet<IPoint> { // 返回接口类型         return LinkedHashSet(pointsLinkedHashSet) // 返回副本，避免外部修改内部集合     }      fun getLastPoint(): IPoint? = pointsLinkedHashSet.lastOrNull() // 返回接口类型      fun clearPoints() = pointsLinkedHashSet.clear()      fun addPoint(latitude: Double, longitude: Double): IPoint { // 返回接口类型         val point = Point(latitude, longitude)         pointsLinkedHashSet.add(point)         return point     }      // private class Point，对外部完全隐藏具体实现     private inner class Point(         override val latitude: Double,         override val longitude: Double     ) : IPoint { // 实现 IPoint 接口         override val radius: Double = this@Sphere.radius          override fun toString(): String {             return "Point(radius=$radius, latitude=$latitude, longitude=$longitude)"         }     } }  // 外部调用示例 fun main() {     val sphere = Sphere(1.0)     val point: IPoint = sphere.addPoint(10.0, 20.0) // 接收 IPoint 接口     println("Point radius = ${point.radius}")     println("Point latitude = ${point.latitude}")      val lastPoint: IPoint? = sphere.getLastPoint()     println("Last Point radius = ${lastPoint?.radius}")      // 编译错误：Cannot access 'Point': it is private in 'Sphere'     // val newPoint = Sphere.Point(30.0, 40.0)      // 编译错误：Unresolved reference: Point     // val concretePoint: Sphere.Point = sphere.addPoint(50.0, 60.0) as Sphere.Point }

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