16. Inheritance

Question 1

What two steps are needed to delete an element in a partially filled array?

Answer 1

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Question 2

What is UML short for?

Answer 2

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Question 3

In the representation for a class, how are public items distinguished from private ones?

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Question 4

What four values are used to generate a colour?

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Question 5

If the relationship ‘A is a B’ is modelled by two classes A and B, which is the superclass and which is the subclass?

Answer 5

A is a subclass
B is a superclass

Question 6

How do we invoke the constructor of the superclass, and when?

Answer 6

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Question 7

When do we invoke the constructor of the superclass implicitly?

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Question 8

What kinds of method can be overridden? Can the new version have a different body? Different parameters? Different name?

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Question 9

What simple errors is the @Override annotation protect us from?

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Question 10

If an object is polymorphic, what does that mean? And how do we achieve it?

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Question 11

In what sense might a method be dynamically bound? Which types of method have this feature?

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Question 12

In what way does a subclass extend its superclass?

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Question 13

How do we make a class abstract, and what can we not do with it when we have made it abstract?

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Question 14

How do we define an abstract method, and when do we? In what sense do we not override an abstract method?

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Question 15

What does it mean to make a method final, and how do we achieve it? What kinds of method can be made final? What about a final class?

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Question 16

How do we create an extension of a class which has more state?

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Question 17

How is the idea of adding more instance methods related to adding more object state?

Answer 17

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Question 18

How do we determine if an object is an instance of a particular class?

Answer 18

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Question 19

What is the essential difference between a class cast and primitive type cast?

Answer 19

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Question 20

Which of the following models ‘is a’ and which models ‘has a’?

1. 
public class DieselTrain extends Train { 
}

2. public class Train {
   private Carriage[] carriages;
   }

Answer 20

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Question 21

When might we want to use an overridden method, and how do we?

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Question 22

What is the purpose of constructor chaining?

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Question 23

When do we invoke another constructor from the same class, and how?

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Question 24

What exactly is a default constructor, and when do we get one?

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Question 25

All classes, except Object, have something. What is that thing?

Answer 25

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Question 26

What does this default Object: toString() produce?

Answer 26

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Question 27

Assuming a point class defined as one might expect, what is the affect of the following code?

System.out.println(new Point(10, 20));

Answer 27

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