September 2017 Update

Task/Polymorphism/Kotlin/polymorphism.kotlin

@@ -0,0 +1,56 @@
+// version 1.1.2
+
+open class Point(var x: Int, var y: Int) {
+    constructor(): this(0, 0)
+
+    constructor(x: Int) : this(x, 0)
+
+    constructor(p: Point) : this(p.x, p.y)
+
+    open protected fun finalize() = println("Finalizing $this...")
+
+    override fun toString() = "Point at ($x, $y)"
+
+    open fun print() = println(this)
+}
+
+class Circle(x: Int, y: Int, var r: Int) : Point(x, y) {
+    constructor(): this(0, 0, 0)
+
+    constructor(x: Int) : this(x, 0, 0)
+
+    constructor(x: Int, r: Int) : this(x, 0, r)
+
+    constructor(c: Circle) : this(c.x, c.y, c.r)
+
+    // for simplicity not calling super.finalize() below though this would normally be done in practice
+    override protected fun finalize() = println("Finalizing $this...")
+
+    override fun toString() = "Circle at center ($x, $y), radius $r"
+
+    override fun print() = println(this)
+}
+
+fun createObjects() {
+    val points = listOf(Point(), Point(1), Point(2, 3), Point(Point(3, 4)))
+    for (point in points) point.print()
+    val circles = listOf(Circle(), Circle(1), Circle(2, 3), Circle(4, 5, 6), Circle(Circle(7, 8, 9)))
+    for (circle in circles) circle.print()
+    println()
+}
+
+fun main(args: Array<String>) {
+    createObjects()
+    System.gc()  // try and force garbage collection
+    Thread.sleep(2000) // allow time for finalizers to run
+    println()
+    val p = Point(5, 6)
+    p.print()
+    p.y = 7  // change y coordinate
+    p.print()
+    val c = Circle(5, 6, 7)
+    c.print()
+    c.r = 8
+    c.print() // change radius
+    /* note that finalizers for p and c are not called */
+}