Inheritance and polymorphism
Quiz
•
Computers
•
University
•
Practice Problem
•
Hard
Christian Dondrup
Used 105+ times
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6 questions
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1.
MULTIPLE CHOICE QUESTION
1 min • 1 pt
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
2.
MULTIPLE CHOICE QUESTION
1 min • 1 pt
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.
3.
MULTIPLE CHOICE QUESTION
1 min • 1 pt
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
4.
MULTIPLE CHOICE QUESTION
1 min • 1 pt
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();
5.
MULTIPLE CHOICE QUESTION
1 min • 1 pt
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.
6.
MULTIPLE SELECT QUESTION
1 min • 1 pt
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
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