CIS 212 Test 1

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| By Xenonii

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Quizzes Created: 4 | Total Attempts: 975

Questions: 9 | Attempts: 77 | Updated: Mar 21, 2023

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Test on CIS 212 including data abstraction, composition, and inheritance

Questions and Answers

1.

An abstract class is a class which
- A.
  
  Doesn't have any implementation of methods
- B.
  
  Has abstract methods but possibly some defined methods as well
- C.
  
  Is only accessed from the same package
- D.
  
  Has only implemented methods
- E.
  
  None of the above
Correct Answer
B. Has abstract methods but possibly some defined methods as well

Explanation
An abstract class is a class that cannot be instantiated and is meant to be extended by other classes. It may have abstract methods, which are methods without any implementation that must be implemented by the subclasses, and it may also have defined methods, which are methods with a complete implementation. Therefore, an abstract class can have a combination of abstract and defined methods.

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2.

Which is the access modifier which makes an element accessible only from the same package or from subclasses
- A.
  
  Public
- B.
  
  Protected
- C.
  
  Package (aka default)
- D.
  
  Private
Correct Answer
B. Protected

Explanation
The access modifier "protected" makes an element accessible only from the same package or from subclasses. This means that any class within the same package can access the protected element, as well as any subclass of the class that contains the protected element, regardless of whether the subclass is in the same package or not. This access modifier provides a level of encapsulation and restricts access to the protected element from classes outside the package or unrelated subclasses.

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3.

In Java how many abstract classes can I extend?
- A.
  
  One
- B.
  
  Two
- C.
  
  Infinite
- D.
  
  You cannot
Correct Answer
A. One

Explanation
In Java you can only extend (inherit) one class, including abstract classes.

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4.

Why is data abstraction important?
5.

When seeing a method signature a lot of information is given. Explain what the following method signature tells the programmer:protected static String reverse(String s)
6.

Why do we have different levels of access modifiers (public, protected, package, private)?
- A.
  
  For making composition possible
- B.
  
  For data abstraction
- C.
  
  For encapsulation and information hiding
- D.
  
  For being able to use inheritance
- E.
  
  None of the above
Correct Answer
C. For encapsulation and information hiding

Explanation
Some elements of a class need to be part of the public interface, however you might want some of the elements to be hidden from certain classes, and not hidden from others. So the programmer has fine control on what is visible to whom

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7.

A method saveFile() throws a FileAlreadyExistsException. Write some code where you would call this method, and handle such an exception by telling the user what the error was and what he can do about it.
8.

Mention the three forms of inheritance, and when each one is used.
9.

What is composition?
- A.
  
  When you extend a class
- B.
  
  When you implement an interface
- C.
  
  When you extend an abstract class
- D.
  
  When an object A has a reference to another object B, and only A has a reference to it. Also A determines lifetime of B.
- E.
  
  When a class calls the super constructors
Correct Answer
D. When an object A has a reference to another object B, and only A has a reference to it. Also A determines lifetime of B.

Explanation
Composition refers to a design pattern in object-oriented programming where one object, A, has a reference to another object, B. In this pattern, only object A has a reference to object B, and it also determines the lifetime of object B. This means that if object A is destroyed or goes out of scope, object B will also be destroyed. Composition is commonly used to create complex objects by combining simpler objects, allowing for code reuse and modularity.

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Current Version
Mar 21, 2023

Quiz Edited by
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Dec 03, 2008

Quiz Created by
Xenonii

CIS 212 Test 1

An abstract class is a class which

Which is the access modifier which makes an element accessible only from the same package or from subclasses

In Java how many abstract classes can I extend?

Why is data abstraction important?

When seeing a method signature a lot of information is given. Explain what the following method signature tells the programmer:protected static String reverse(String s)

Why do we have different levels of access modifiers (public, protected, package, private)?

A method saveFile() throws a FileAlreadyExistsException. Write some code where you would call this method, and handle such an exception by telling the user what the error was and what he can do about it.

Mention the three forms of inheritance, and when each one is used.

What is composition?