/** * Lab 3: Point and MovablePoint - Inheritance with Behavior * PT821 - Object-Oriented Programming * State University of Zanzibar (SUZA) * * LEARNING OBJECTIVES: * - Add behavior to existing classes through inheritance * - Access private parent attributes through getters/setters * - Understand why subclass cannot directly access private parent variables * - Apply method overriding for extended functionality * * INSTRUCTIONS: * Complete the following exercises step by step. * Follow the TODO comments and implement the required functionality. */ // ============================================================ // PART A: The Point Class (Superclass) // ============================================================ /* * TODO 1: Create a class called "Point" with: * * Private instance variables: * - x (double, default 0.0) * - y (double, default 0.0) * * Constructors: * - Point() - default (0.0, 0.0) * - Point(double x, double y) * * Public methods: * - getX(), setX(double x) * - getY(), setY(double y) * - setXY(double x, double y) - sets both x and y * - getXY() - returns double[] containing {x, y} * - toString() - returns "(x, y)" e.g., "(3.0, 4.0)" */ // Write your Point class here: // ============================================================ // PART B: The MovablePoint Class (Subclass of Point) // ============================================================ /* * TODO 2: Create a class called "MovablePoint" that extends Point with: * * Private instance variables: * - xSpeed (double, default 0.0) * - ySpeed (double, default 0.0) * * Constructors: * - MovablePoint() - default values * - MovablePoint(double xSpeed, double ySpeed) * - MovablePoint(double x, double y, double xSpeed, double ySpeed) * Must call super(x, y) * * Public methods: * - getXSpeed(), setXSpeed(double xSpeed) * - getYSpeed(), setYSpeed(double ySpeed) * - setSpeed(double xSpeed, double ySpeed) * - getSpeed() - returns double[] containing {xSpeed, ySpeed} * * - move() - moves the point by adding speed to position: * IMPORTANT: You CANNOT write "x += xSpeed" because x is private in Point * You MUST use: setX(getX() + xSpeed) and setY(getY() + ySpeed) * Returns this (the MovablePoint itself) for method chaining * * - @Override toString() - returns "(x, y) speed=(xSpeed, ySpeed)" * e.g., "(3.0, 4.0) speed=(1.0, 2.0)" */ // Write your MovablePoint class here: // ============================================================ // PART C: Test Driver // ============================================================ public class Lab3_PointMovablePoint { public static void main(String[] args) { System.out.println("==============================================="); System.out.println(" Lab 3: Point and MovablePoint"); System.out.println("===============================================\n"); // ----- Section 1: Point Objects ----- System.out.println("--- Section 1: Point Objects ---"); // TODO 3: Create and test Point objects // Point p1 = new Point(); // System.out.println("Default point: " + p1); // // Point p2 = new Point(3.0, 4.0); // System.out.println("Point at (3, 4): " + p2); // // p2.setX(5.0); // p2.setY(6.0); // System.out.println("After setX(5), setY(6): " + p2); // // double[] coords = p2.getXY(); // System.out.println("getXY() = [" + coords[0] + ", " + coords[1] + "]"); // ----- Section 2: MovablePoint Objects ----- System.out.println("\n--- Section 2: MovablePoint Objects ---"); // TODO 4: Create a MovablePoint and test basic properties // MovablePoint mp1 = new MovablePoint(0.0, 0.0, 2.0, 3.0); // System.out.println("Initial position: " + mp1); // // // Inherited methods from Point // System.out.println("X coordinate: " + mp1.getX()); // System.out.println("Y coordinate: " + mp1.getY()); // ----- Section 3: Movement ----- System.out.println("\n--- Section 3: Movement ---"); // TODO 5: Demonstrate the move() method // System.out.println("Before move: " + mp1); // mp1.move(); // System.out.println("After 1st move: " + mp1); // mp1.move(); // System.out.println("After 2nd move: " + mp1); // mp1.move(); // System.out.println("After 3rd move: " + mp1); // TODO 6: Change speed and continue moving // mp1.setSpeed(1.0, -1.0); // System.out.println("\nSpeed changed to (1.0, -1.0)"); // mp1.move(); // System.out.println("After move: " + mp1); // mp1.move(); // System.out.println("After move: " + mp1); // ----- Section 4: Polymorphism with Point ----- System.out.println("\n--- Section 4: Polymorphism ---"); // TODO 7: A MovablePoint IS-A Point // Point p3 = new MovablePoint(1.0, 1.0, 0.5, 0.5); // System.out.println("p3 (Point ref): " + p3); // System.out.println("p3 class: " + p3.getClass().getSimpleName()); // // // Can we call move() on p3? Why or why not? // // p3.move(); // Uncomment to test - does it compile? // // ANSWER: _______________________________________________ // // // Downcast to call move() // if (p3 instanceof MovablePoint) { // MovablePoint mp2 = (MovablePoint) p3; // mp2.move(); // System.out.println("After downcast and move: " + mp2); // // Notice: p3 also reflects the change (same object!) // System.out.println("p3 also changed: " + p3); // } // ----- Section 5: Simulation ----- System.out.println("\n--- Section 5: Simple Movement Simulation ---"); // TODO 8: Create multiple moving points and simulate movement // MovablePoint[] points = { // new MovablePoint(0.0, 0.0, 1.0, 1.0), // moves diagonally // new MovablePoint(10.0, 0.0, -1.0, 0.5), // moves left and slightly up // new MovablePoint(5.0, 5.0, 0.0, -2.0) // moves straight down // }; // // System.out.println("Starting positions:"); // for (int i = 0; i < points.length; i++) { // System.out.println(" Point " + (i + 1) + ": " + points[i]); // } // // // Simulate 5 steps of movement // for (int step = 1; step <= 5; step++) { // System.out.println("\nStep " + step + ":"); // for (int i = 0; i < points.length; i++) { // points[i].move(); // System.out.println(" Point " + (i + 1) + ": " + points[i]); // } // } System.out.println("\n==============================================="); System.out.println(" End of Lab 3"); System.out.println("==============================================="); } } /* * EXPECTED OUTPUT (after completing all TODOs): * * =============================================== * Lab 3: Point and MovablePoint * =============================================== * * --- Section 1: Point Objects --- * Default point: (0.0, 0.0) * Point at (3, 4): (3.0, 4.0) * After setX(5), setY(6): (5.0, 6.0) * getXY() = [5.0, 6.0] * * --- Section 2: MovablePoint Objects --- * Initial position: (0.0, 0.0) speed=(2.0, 3.0) * X coordinate: 0.0 * Y coordinate: 0.0 * * --- Section 3: Movement --- * Before move: (0.0, 0.0) speed=(2.0, 3.0) * After 1st move: (2.0, 3.0) speed=(2.0, 3.0) * After 2nd move: (4.0, 6.0) speed=(2.0, 3.0) * After 3rd move: (6.0, 9.0) speed=(2.0, 3.0) * * Speed changed to (1.0, -1.0) * After move: (7.0, 8.0) speed=(1.0, -1.0) * After move: (8.0, 7.0) speed=(1.0, -1.0) * * --- Section 4: Polymorphism --- * p3 (Point ref): (1.0, 1.0) speed=(0.5, 0.5) * p3 class: MovablePoint * After downcast and move: (1.5, 1.5) speed=(0.5, 0.5) * p3 also changed: (1.5, 1.5) speed=(0.5, 0.5) * * --- Section 5: Simple Movement Simulation --- * Starting positions: * Point 1: (0.0, 0.0) speed=(1.0, 1.0) * Point 2: (10.0, 0.0) speed=(-1.0, 0.5) * Point 3: (5.0, 5.0) speed=(0.0, -2.0) * * Step 1: * Point 1: (1.0, 1.0) speed=(1.0, 1.0) * Point 2: (9.0, 0.5) speed=(-1.0, 0.5) * Point 3: (5.0, 3.0) speed=(0.0, -2.0) * ... (continues for 5 steps) * * QUESTIONS TO ANSWER: * 1. Why can't MovablePoint directly access x and y (e.g., x += xSpeed)? * 2. What is the advantage of using getters/setters to access parent fields? * 3. In Section 4, why does changing mp2 also change p3? * 4. Could you make move() work through a Point reference without downcasting? * What design change would be needed? * * SUBMISSION: * - Complete all TODO sections * - Answer all questions above in comments * - Submit the completed .java file */