Encapsulation

Question 1

What is information hiding?

Answer 1

Question 2

In a C++ class, what does public:, private:, protected: mean?

Answer 2

Question 3

In C++, what is the difference between private and protected? Why use one over the other?

Answer 3

Question 4

This is an example of the incorrect way to code: What would be the proper way to isolate what should be class A’s own data member?

Answer 4

Question 5

Mutators should generally not be just assigning a value. What should they be doing in addition to?

Answer 5

Question 6

When defining a subclass, what do the following do?

• class B : public A
• class B : private A
• class B: protected A

Answer 6

Question 7

How would you take the following code, and modify it with inheritance permissions to make a proper stack?

Answer 7

Note: this is still not a good place to use inheritance, the type is not substitutable: A stack is not a subtype of list and can’t serve as a substitute for a list. The correct way to do this would be to use containment(i.e. build the list, then use it as a data member inside a stack).

Question 8

Consider this code, what’s a better way to code this using iteration?

Answer 8

Make theItem, link public in Node?

• works but defeats the purpose of encapsulation (anybody could use them then).

Make theItem, link protected in node?

• Subclasses could access them then!
  
  • but that doesn’t help, because GenericList is NOT a subclass of Node

SOLUTION:

• Friendship!

Question 9

C++ friends

1. In general how does the friend statement work?
2. What does the friend satement allow?

Answer 9

1. A friend statement notes the name/signature of a class/function that is meant to have a special relationship to this class
2. Allows that class/function access to the class’ private member and makes it part of the object’s scope (allowing it to use the object’s members!)

Question 10

Provide a code example in a class using friend

Answer 10

Question 11

In general, how do you achieve friendship (from C++) in Java?

Answer 11

Question 12

In general, what is a Java package and how does it work?

Answer 12

Question 13

What is the specific code syntax for packages in Java?

Answer 13

Question 14

In the following code:

1. What is the name of the package?
2. What is it’s directory and where must it reside?

Answer 14

Question 15

How would you add another file to the package attached?

Answer 15

Question 16

In the following code, what does the public and non-public mean?

Answer 16

Question 17

How would you import the attached java package?

Answer 17

We can also import only a single class from a package by substituting its name for the wildcard(*)

Question 18

If I am not using any Java packages, we don’t need to care about any of the package details?

Answer 18

Question 19

What should always be part of classpath, so placement inside the current folder should always work?

Answer 19

.(the current folder)

Question 20

If we don’t define a superclass implementation for a (non-pure) virtual method, we get what type of error?

Answer 20

Question 21

For a linker error, why can’t C++ catch this error at compile time?

Answer 21

Question 22

Why use packages in Java?

Answer 22

Question 23

In Java protection modes, what does Public mean?

Answer 23

Visible to anybody anywhere

Question 24

In Java protection modes, what does Protected mean?

Answer 24

Question 25

In Java protection modes, what does Private mean?

Answer 25

Visible only to the class in which it’s defined

Question 26

In Java protection modes, what does Blank(supply no protection info at all) mean?

Answer 26

Question 27

What would the folder structure look like for the following code?

Answer 27

Question 28

For the attached code, can either class access defaultInt? Why?

Answer 28

Question 29

For the attached code, can either class access privatetInt? Why?

Answer 29

Question 30

For the attached code, can either class access protectedInt or publicInt? Why?

Answer 30

This shows you that protected is in fact a lot more insecure than you would at first think.

That’s why data members shouldn’t be protected, as we’ve already discussed. They should be private, with protected accessors/mutators that can be inherited by children (or blank/friendly, so those in the same package can access!)

• and hopefully high level intelligent methods rather than just blunt gets/sets
• … and simulatly, these accessors/mutators could be blank(package-private), to allow anybody in the same package(presumably there for the same purpose!) to use them

Question 31

What is the difference between Protected and package protection?

Answer 31

Question 32

For the attached code, why can’t class OutsideTest access x.defaultInt?

Answer 32

Question 33

For the attached code, in class OutsideTest why can’t ProTest access privateInt?

Answer 33

Question 34

For the attached code, in class OutsideSubClass why can’t it access OtherClass x or defaultInt? Even though it extends ProTest?

Answer 34

the class IS related to ProTest but it’s in a different package (default/unamed package)

Question 35

Why can OutsideSubClass access protectedInt?

Answer 35

Question 36

Answer 36

Question 37

In reference to Java and protected, what is worthwhile remembering regarding the underlying implementation?

Answer 37

Question 38

In general, what is the object pointer?

Answer 38

Question 39

For the following code, if you want to invoke dostuff form inside whater, and supply the object itself as an argument, what code would you use?

Answer 39

dostuff(this);

Question 40

For the following code, what is p REALLY doing?

Answer 40

Question 41

In Python, how does self reference work?

Answer 41