ITSC 1213 - Introduction to CS 2 How to Design Programs with Object Oriented Programming

 // Method that accepts any object fulfilling the Vehicle contract
public static void simulateMovement(Vehicle v, double timeStep) {
    // We can safely call methods defined in the Vehicle contract
    v.updatePosition(timeStep); // Assumes updatePosition is in Vehicle
    System.out.println(
        "Vehicle moved. Current speed: " + v.getSpeed() // Assumes getSpeed is in Vehicle
    );
    // We cannot call v.openTrunk() or v.ringBell() here,
    // because those are not part of the base Vehicle contract.
}

// We can call this method with different Vehicle subtypes
Car myCar = new Car(/*...*/);
Bicycle myBike = new Bicycle(/*...*/);
Motorcycle myMotorcycle = new Motorcycle(/*...*/);

simulateMovement(myCar, 0.1);        // Works! Car 'is-a' Vehicle
simulateMovement(myBike, 0.1);       // Works! Bicycle 'is-a' Vehicle
simulateMovement(myMotorcycle, 0.1); // Works! Motorcycle 'is-a' Vehicle

 // Method that accepts any object fulfilling the Drawable contract
public static void renderOnScreen(Drawable item) {
    System.out.println("Preparing to draw...");
    // We can safely call methods defined in the Drawable contract
    item.draw(); // The actual draw() method executed depends on the runtime type of 'item'
    System.out.println("...drawing complete.");
    // We cannot call item.getRadius() or item.getWidth() here,
    // as those are specific to implementing classes, not the Drawable contract.
}

// Assume Circle, Rectangle, and FancyButton all implement Drawable
Circle circle = new Circle(/*...*/);
Rectangle rectangle = new Rectangle(/*...*/);
FancyButton button = new FancyButton(/*...*/); // Even UI elements can be Drawable

renderOnScreen(circle);    // Works! Circle implements Drawable
renderOnScreen(rectangle); // Works! Rectangle implements Drawable
renderOnScreen(button);    // Works! FancyButton implements Drawable

// Assume ArrayList has been introduced
// Using List<Vehicle> ensures only Vehicle objects (or subclasses) can be added
java.util.List<Vehicle> traffic = new java.util.ArrayList<>();

traffic.add(new Car(...));
traffic.add(new Bicycle(...));
traffic.add(new Car(...));
traffic.add(new Motorcycle(...));

// Process all vehicles uniformly using the Vehicle contract
System.out.println("Updating all vehicle positions:");
for (Vehicle v : traffic) {
    // This works because every object in the list guarantees
    // it fulfills the Vehicle contract, which includes accelerate()
    v.accelerate(0.5); // Apply gentle acceleration to all
    simulateMovement(v, 0.5); // Reuse our previous method
}