Anatomy of a Class Practice Test

Considering the Java class example below, which statement best describes polymorphism?

public class Animal {

  public void speak() {

    System.out.println("...");

  }

}

public class Dog extends Animal {

  @Override

  public void speak() {

    System.out.println("Woof");

  }

}

public class Cat extends Animal {

  @Override

  public void speak() {

    System.out.println("Meow");

  }

}

class Demo {

  public static void main(String[] args) {

    Animal a1 = new Dog();

    Animal a2 = new Cat();

    a1.speak();

    a2.speak();

  }

}

// Encapsulation: hide fields using private.

// Inheritance: Dog and Cat extend Animal.

// Polymorphism: the same call can run different overridden methods.

Based on the class structure presented above, which best describes polymorphism here?

Considering the Java class example below, why is it important to use methods like start() in a class structure?

public class Car {

  private boolean running;

  public Car() {

    running = false; // constructor sets initial state

  }

  public void start() {

    // behavior changes state safely

    running = true;

  }

  public void stop() {

    running = false;

  }

}

// Encapsulation: running is private; methods change it.

// Inheritance: a subclass could extend Car.

// Polymorphism: a subclass could override start().

Based on the class structure presented above, why use methods like start()?