CS302/15 Questions on OO and Java
Question 1 Basic OO Knowledge
a. What is a class, what is an object, and what is the relation between an object and its class?
b. Which UML class diagram below shows a class and which an object?
![[A] or [:B]?](16/ole1.gif)
c. Describe the differences between an instance variable and a class variable.
d. Fill in the blanks: Object-Oriented programming differs from using data abstraction because OO uses (1) i___________________ and (2) p_________________.
e. Describe over-riding.
/** Simplest demo of polymorphism
*/
import java.lang.*;
class Hello1 {
public void print(){
System.out.println("Hello1");
}//Hello1.print
}//class Hello1
class Hello2 extends Hello1{
public void print(){
System.out.println("Hello2");
}//Hello2.print
public static void main(String argv[]){
(new Hello1()).print();//which print do we get?
(new Hello2()).print();//which print do we get?
Hello1 hiThere = new Hello2();
hiThere.print();//which print do we get?
}//main
}//class Hello2
Answer: Try it in the lab!
Warm Stretch Part 2
I translate the above Java into C++ in the obvious way (see below), compile
it, and run it. What happens?
/* Simplest demo of polymorphism: Hello1.cpp
*/
#include <iostream>
using namespace std;
class Hello1 {
public:
void print(){
cout <<"Hello1"<<endl;
}//Hello1.print
};//class Hello1
class Hello2:public Hello1{
public:
void print(){
cout <<"Hello2"<<endl;
}//Hello2.print
};//class Hello2
int main(){
(new Hello1())->print();//which print do we get?
(new Hello2())->print();//which print do we get?
Hello1 * hiThere = new Hello2();
hiThere->print();//which print do we get?
}//main
Suprise! Try it in the lab.....
I add the reserved word "virtual" as shown below, compile it, and run it. What happens?
/* Simplest demo of polymorphism: Hello1.cpp
*/
#include <iostream>
using namespace std;
class Hello1 {
public:
virtual void print(){
cout <<"Hello1"<<endl;
}//Hello1.print
};//class Hello1
class Hello2:public Hello1{
public:
void print(){
cout <<"Hello2"<<endl;
}//Hello2.print
};//class Hello1
int main(){
(new Hello1())->print();//which print do we get?
(new Hello2())->print();//which print do we get?
Hello1 * hiThere = new Hello2();
hiThere->print();//which print do we get?
}//main
The above works just like the first Java program.....
The above exercises demonstrate P____________________________.
a. Define a concrete class and an abstract class (one sentence each).
b. What is an interface?(one sentence)
c. Show how an abstract class, an interface, and a client using an interface are drawn in the UML.
Answer: [ ole2.gif ]
d. What can you do with a concrete class that you cannot do with a more abstract class? (sentence)
[ ole3.gif ]
a. Describe polymorphism.
b. Define and explain the differences between: static binding and dynamic binding of methods.
c. To get polymorphism which method binding do you need: static or dynamic?
d. What word is used to get dynamic binding in C++? Fill in the blank: v_____________.
d. Give C++ code that gives different answers depending only on whether dynamic binding is used.
e. In Java, are methods polymorphic or not? Do you have a choice? If so, how do you exercise your choice?
Question 4 Java
a. What is Java?
b. Give a short history of Java.
c. What questions would a typical C++ programmer ask when they start learning Java?
d. In Java what are the differences between an application and an applet? (short 4 sentence essay)
Question 5 OO Issues
List and describe the design issues for Object-Oriented
programming languages.
Question 6 History of OOPL
Write a brief history of Object-Oriented programming including
dates and names of languages and people.
Question 7 History of OOPL
Draw a time-line(picture) of the development of Object-Oriented
programming.