Inheritance and polymorphism

The method of which class is called in the example below?

class A {

public void method() {...};

}

class B extends A {

public void method() {...};

}

class C extends B {

public void method() {...};

}

A obj = new C();

((B)obj).method();

• The method in A

• The method in B

• The method in C

• None of them; throws exception

What type of error does this produce and why?

class Animal() {}

class Dog extends Animal {}

Dog dog = new Animal();

• Compiler error; Because the dynamic type is the super class of the static type.

• Compiler error; Because the static type is the super class of the dynamic type.

• Runtime error; Because the dynamic type is the super class of the static type.

• Runtime error; Because the static type is the super class of the dynamic type.

What type of casting does the following piece of code use?

class Car {}

class SportsCar extends Car {}

Car car = new SportsCar();

• Automatic downcasting

• Automatic upcasting

• Manual downcasting

• Manual upcasting

Assuming the class structure below, which of the following pieces of code correctly prints "Meow!"?

class Animal {}

class Cat extends Animal {

public void speak() {

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

}

}

...

Animal a = new Cat();

• speak();

• Animal.speak();

• Cat.speak();

• a.speak();

• ((Cat)a).speak();

What does type loss mean in the context of Java?

• When manually casting using the static type in brackets before the name of a variable, it loses its dynamic type.

• During downcasting the static type of the variable is replaced by the dynamic type of the obejct, therefore, the variable loses its type.

• During upcasting the object assumes the static type of the variable and, therefore, loses its own static type.

• When creating a subclass, the superclass loses its type and, therefore, the static type of the superclass becomes the dynamic type of the subclass.

Select all statements about ArrayLists that are true.

• They are polymorphic

• They are of fixed length

• They are dynamic in length

• They provide iterators

• They can hold objects and simple data types such as int, double, boolean