Unit_1

Question 1

the difference is between
a record and a class?

Answer 1

Records don’t support:
1. Encapsulation (restricting access to some fields,
information hiding)
2. Variables, behaviours at the class level (class variables,
class methods – “static” in Java)
3. Relationships to other classes (hierarchies,
inheritance)

Question 2

What is an ADT?

Answer 2

Abstract Data Type (ADT):
◦ Structure the data in a useful fashion
◦ Keep its interface (how we interact with it) separated
completely from its implementation (the details of how
the operations and structuring is done)
◦ The point of the abstraction is to remove users from the
burden of understanding how things are dealt with
inside the data structure

Question 3

What is a message?vv

Answer 3

• An important idea of OOP is messaging: messages are
  sent to an object (by calling its methods), and then the
  object responds
• Messages can have parameters:
  ◦ E.g.: create student named x with studentID y
• Sender of the message (client)
  ◦ doesn’t know what actions will be done internally
  ◦ doesn’t know what methods the receiver will use to
  satisfy the requirements of the message
  ◦ doesn’t need to know/care/worry about this

Question 4

If you want access to private members of the superclass inside the subclass, you can:

Answer 4

◦ Use accessor/mutator (get/set) methods
▪ Still a good reliable secure way to do it
◦ Declare the variables as protected instead of private in
the superclass
▪ This says “allow subclasses of this class to use this, too”
* This applies to methods, too,

Question 5

GraphicalObject go = new Button();
What is the static type of go?
The dynamic type?

Answer 5

GraphicalObject go = new Button();

◦ The static type of go is GraphicalObject
◦ The (actual) dynamic type is Button
▪ what the variable is actually storing can be the same
class (static type) or any subclass → it must be looked
up at run time

Question 6

How would you explain dynamic class binding in
one sentence?

Answer 6

Dynamic class binding refers to the process where the method or function call is resolved at runtime, based on the actual object type rather than the declared type.

class Animal {
void sound() {
System.out.println(“Animal sound”);
}
}

class Dog extends Animal {
@Override
void sound() {
System.out.println(“Bark”);
}
}

public class Main {
public static void main(String[] args) {
Animal myAnimal = new Dog(); // Dynamic binding
myAnimal.sound(); // Output: Bark
}
}
Here, myAnimal.sound() calls the sound() method from the Dog class at runtime, even though the reference type is Animal.

Question 7

How would you explain dynamic method-
message mapping in one sentence?

Answer 7

Dynamic method-message mapping refers to the process where a method is selected and invoked based on the actual type of the object at runtime, rather than the type of the reference variable.

Question 8

What do you think are some advantages of
object-oriented programming?

Answer 8

• Software and Code Reusability
• Understandability and Maintenance
• Ease of Design