Basic OO concepts in Java/C++

Question 1

For what languages are pointers implicit?

Answer 1

Java and Ruby

Question 2

For what language are pointers handled explicitly?

Answer 2

C/C++

Question 3

In Java what thing does the linkedList structure look like?

Answer 3

Question 4

How do Ruby variables work?

Answer 4

Question 5

How do you declare a pointer, allocate memory and set the variable in C/C++?

Answer 5

int * ptr;

ptr = malloc(sizeof(int));

*ptr = 5;

Question 6

How do you use a pointer in C/C++ of an existing variable.

Answer 6

int x = 5;

int * intptr = &x;

Question 7

How does the -> operator work in C++

int value = myList->data;

How would you access myLists’s print method?

Answer 7

It dereferences myList, then get the “data” field.

It would be shorthand for (*myList).data, the brackets are required to ensure the dereferncing is done first.

myList->print( ) is equal to (*myList).print( )

Question 8

How do you return the memory memory when you are done with an object in C++?

How does it work?

Answer 8

Question 9

In general how do pointer types work in most languages?

Answer 9

Question 10

How do you cast a pointer to another type and why is it a bad idea?

Answer 10

Question 11

How do you define a class in Java? (what is the code)

Answer 11

Question 12

How do you define a class in C++ (the code in one file)

Answer 12

Question 14

What is a null constructor and how are they used in a class?

Answer 14

Question 15

What does it mean for a constructor to be overloaded? How does this affect the null constructor?

Answer 15

Question 16

What is the unique way constructors are used in C++ that can increase the speed of initialization?

What is the specific code?

Answer 16

Question 17

What are the advantages of using door(numdoor) vs door = numdoor (objects as fields)

Answer 17

Question 18

How do you use a class in Java?

Answer 18

Question 19

What does the public setting in a class do?

Answer 19

A public class makes it visible from the outside world - it can have a main( ) method that will be invoked. However you can only have one public class.

Question 20

In java, how do you create a new object and how do you access the object fields or methods

Answer 20

Question 21

How do you compile in general with g++?

How do you compile and name the a.out file at the same time?

Answer 21

g++ myfile.cpp

add -0 <filename></filename>

g++ myfile.cpp -o myprogram

Question 22

What is a namespace and how is it used?

Answer 22

Question 23

In C++ code a simle node class

Answer 23

Question 24

In C++ what is the code for a simple list class?

Answer 24

Question 25

What are the C++ nodes and list methods code?

Answer 25

Question 26

In general, how does main work in C++?

Answer 26

Question 27

Give an example of coding main in C++

Answer 27

Question 28

What are extraction operators and how do they work?

Answer 28

Question 29

When using classes in C++, when do we need to use unqualified vs qualified names?

Answer 29

Question 30

What is an example of and code fr a heap-based object in C++?

Answer 30

Question 31

What is an example of and code for a stack-based object in C++?

Answer 31

Question 32

In C++ stack vs heap based objects, why use one over the other?

Answer 32

Question 33

What is the diagram for class hierachy for our general linkedlist example?

Answer 33

Question 34

Using Java and our linkedlist example, what is the code for the Node class?

Answer 34

Question 35

In general, what is a concrete class and what is an abstract class (in Java)

Answer 35

**Concrete** - fully implemented, meant to be instantiated **Abstract** - providing elements to be inherited by subclasses, not meant to be instaniated itself * defined by adding the keyword abstract (abstract class ListItem{...) * even though you can never create an instance of an abstract class, we can define constructors * theses constructors are there to assist with inheritance

Question 36

using print( ) as an example, we have an abstract class: ListItem. How do you enforce the need for subclasses of ListItem to have a print method

Answer 36

Question 37

Can a method be defined as abstract in a concrete class? Why?

Answer 37

Question 38

In our ListItem example, what is the code for subclass for intAtom? (in Java)

Answer 38

Question 39

In our ListItem example, what is the subclass Java code for Intchar?

Answer 39

Question 40

In our ListItem example, what is the subclass code for GenericList?

Answer 40

Question 41

What is happening in the following code?

Answer 41

Question 42

How does Dynamic Class binding work with the ListItem?

Answer 42

Question 43

What is polymorphism and what are the benefits?

Answer 43

Question 44

How do signatures work with abstract classes and subclasses?

Answer 44

Question 45

Why do abstract classes exist?

Answer 45

Question 46

Why can't you use ( ) at the end of a stack based null constructor in C++?

Answer 46

putting ( ) will turn it into a forward reference(used in separate compilation)