OOP

Question 1

What is the general nature of an object?

Answer 1

An object encapsulates data (state) and behavior (methods), with its own identity and is created from a class.

Question 2

What is an abstract entity?

Answer 2

A generalized concept (like an abstract class or interface) that cannot be instantiated, and is used to define structure or behavior that other concrete classes must implement.

eg. “animal” is an abstract entity. You don’t see animals around, you see dogs, birds, cats, etc.

Question 3

What is the difference between an object and an instantiation?

Answer 3

Instantiation is the process of creating an object from a class. An object is the result of that process—an actual instance of the class with its own state and behavior.

Question 4

What is instantiation?

Answer 4

The process of creating an object from a class by calling its constructor, which allocates memory and initializes its attributes.

Example: Car myCar = new Car();

Question 5

What is a UML (unified modelling language) diagram?

Answer 5

A standardized visual representation of a system’s classes, objects, and their relationships, used to model object-oriented programs.

Question 6

What is the process of decomposition into several related objects?

Answer 6

It’s the process of dividing a complex problem or system into simpler, connected objects, where each object handles its own specific task.

Question 7

What is dependency (‘uses’) in object-oriented programming?

Answer 7

A relationship where one class depends on another to function, typically by calling its methods or using its data temporarily.

Question 8

What is aggregation (‘has a’)?

Answer 8

A relationship where one class contains or is composed of other classes, but those parts can exist independently of the whole.

Question 9

What is inheritance (‘is a’)?

Answer 9

A mechanism where one class (subclass) inherits attributes and methods from another class (superclass), allowing code reuse and hierarchical relationships.

Question 10

Why is it important to reduce dependencies in a given problem?

Answer 10

Dependencies increase maintenance overheads.

Question 11

Why is it necessary to have different data types?

Answer 11

To accurately and efficiently represent and manipulate different kinds of data in a program. Each type defines the kind of values a variable can store, how much memory it uses, and what operations can be performed on it.

Question 12

What is an integer?

Answer 12

A data type used to store whole numbers, both positive and negative, without decimals.

Question 13

What is a real data type?

Answer 13

A data type used to store numbers with decimal (fractional) parts, including both positive and negative values.

Question 14

What is a string?

Answer 14

A data type used to store a sequence of characters, such as letters, numbers, and symbols.

Question 15

What is a boolean?

Answer 15

A data type that can store only two possible values: true or false.

Question 16

What are parameters in programming?

Answer 16

Parameters are placeholders used in sub-programs (like procedures or functions) to receive data (input) from the part of the program that calls them.

Question 17

How are data items passed to and from parameters?

Answer 17

Pass by value
When you pass a variable to a method, a copy of the value is passed — not the original.
So if you change it inside the method, the original doesn’t change.

🧠 Example: If you pass x = 5 to a function and the function changes it to 10, x is still 5 outside the function.
(There is another method called pass-by-reference but you don’t need to understand this)

Question 18

What is encapsulation?

Answer 18

The concept of bundling data and methods that operate on that data into a single class, and restricting direct access to some components using access modifiers (e.g. private, public).

Question 19

What is polymorphism?

Answer 19

Polymorphism allows objects of different classes to be treated as if they are of the same class, usually through shared methods.

Question 20

What is method overloading?

Answer 20

Defining multiple methods with the same name but different parameters within the same class.

Question 21

What is method overriding?

Answer 21

When a subclass provides a new implementation of a method inherited from its superclass, using the same method name and parameters.

Question 22

What are the advantages of encapsulation?

Answer 22

The scope of data should be confined to the object in which it is defined as far as possible in order to limit side effects and dependencies

Keeps data protected from unauthorized access or accidental changes and improves code maintainability by controlling how data is accessed and modified.

Question 23

What are the advantages of inheritance?

Answer 23

A parent object holds common data and actions, which enhances reuse and reduces maintenance overheads.

Promotes code reuse by allowing new classes to use existing class functionality and simplifies updates: changes in the parent class automatically affect child classes.

Question 24

What are the advantages of polymorphism?

Answer 24

An action in a child object may choose to override actions of a parent object. This allows an external program to use the same action on a family of objects without knowing the implementation detail.

Improves flexibility and extensibility of code and enables generic code that works on objects of different types.

Question 25

What are the advantages of libraries of objects?

Answer 25

Sorts and other complex algorithms and processes do not have to be “re-invented” Saves development time through reusable, pre-tested components and encourages consistency and reliability across projects.

Question 26

What are the disadvantages of OOP?

Answer 26

Increased complexity for small problems. Can be more complex and harder to learn than procedural programming and may use more memory and processing power due to additional structures.

Question 27

What is the use of programming teams?

Answer 27

Working in teams improves productivity, problem-solving, and allows members to specialize in different tasks (e.g. front-end, back-end, testing).

Question 28

What is modularity in program development?

Answer 28

Modularity means dividing a program into separate, independent components (modules), each responsible for a specific task.

Question 29

What are the advantages of modularity?

Answer 29

Makes code easier to understand, debug, and maintain; allows multiple developers to work on different parts of the program at the same time; promotes code reuse and easier testing.

Question 30

What is a class?

Answer 30

A template or blueprint for creating objects. It defines the attributes (variables) and methods (functions) that the objects will have.

Question 31

What is an identifier?

Answer 31

An identifier is the name you give to a class, object, method, or variable in code.

Question 32

What is an instance variable?

Answer 32

A variable defined in a class but outside any method, and each object created from the class has its own copy. ie. one specific attribute or piece of data that belongs to a particular object.

Question 33

What is a parameter variable?

Answer 33

A variable declared in a method signature to receive values when the method is called.

Question 34

What is a local variable?

Answer 34

A variable that’s declared inside a method and only exists while that method is running — you can’t use it outside that method.

Question 35

What is a method?

Answer 35

A function defined in a class that performs actions or returns values when called on an object.

Question 36

What is an accessor (get method)?

Answer 36

A method that returns the value of an instance variable without changing it.

Question 37

What is a mutator (set method)?

Answer 37

A method that changes the value of an instance variable.

Question 38

What is a constructor?

Answer 38

A special method that is called when an object is created, used to initialize instance variables.

Question 39

What is a method signature?

Answer 39

The combination of a method’s name and parameter list — used to identify the method.

Question 40

What is a return value?

Answer 40

The output value that a method sends back after execution, if it is not void.

Question 41

What does 'private' mean in access modifiers?

Answer 41

Accessible only within the same class.

Question 42

What does 'protected' mean in access modifiers?

Answer 42

Accessible within the class, subclasses, and same package.

Question 43

What does 'public' mean in access modifiers?

Answer 43

Accessible from any class.

Question 44

What does 'extends' mean in class inheritance?

Answer 44

Keyword used when one class inherits from another class.

Question 45

What does 'static' mean?

Answer 45

static means a variable or method belongs to the class itself, not individual objects, so it's shared across all objects, and any change to it affects all of them.

Question 46

What is the int data type?

Answer 46

Stores integers.

Question 47

What is the long data type?

Answer 47

Stores large integers.

Question 48

What is the double data type?

Answer 48

Stores decimal values.

Question 49

What is the char data type?

Answer 49

Stores a single character.

Question 50

What is the boolean data type?

Answer 50

Stores true/false.

Question 51

What are features of modern programming languages that enable internationalization?

Answer 51

Unicode for global text support and locale settings for date, time, and currency formats.

Question 52

What are the ethical & moral obligations of programmers?

Answer 52

Ensure data privacy and security and avoid bias in algorithms.

Question 53

What are selection statements in programming?

Answer 53

Selection statements let your program make decisions and choose what code to run based on conditions. Use if, if-else, or switch to control flow.

Question 54

What are repetition statements in programming?

Answer 54

Use for, while, or do-while loops for repetition.

Question 55

What are static arrays?

Answer 55

A static array is an array with a fixed size that cannot be changed after it is created. - Fixed-size collection of elements of the same type.

Question 56

What is a primitive data type?

Answer 56

A primitive data type is a fundamental data type provided by a programming language to store simple values such as integers, characters, or booleans.

Question 57

What is a method signature?

Answer 57

A method signature is the part of a method definition that includes the method’s name and the number and type of its parameters.

Question 58

What is runtime error?

Answer 58

A runtime error is an error that occurs while the program is running, causing it to crash or behave unexpectedly. Examples include: * Dividing by zero * Accessing an invalid array index * Using a null reference These errors are not detected during compilation but only appear when the affected code is executed.

Question 59

What is the purpose of "this."?

Answer 59

The purpose of this. is to refer to the current object’s instance variables or methods within a class. It is commonly used to distinguish between instance variables and parameters or local variables with the same name.

Question 60

What is open source code?

Answer 60

Open source code is source code that is made freely available for anyone to view, use, modify, and distribute. Source code is the original human-readable code written by a programmer in a high-level programming language, such as Java or Python.

Question 61

Ethical issues that may arise if modules are developped from open source code

Answer 61

* License violations: Reusing open source code without following its license terms (e.g., not crediting authors or failing to share modifications) can be unethical and possibly illegal. * Lack of attribution: Failing to acknowledge original developers disrespects their intellectual contributions. * Security risks: Using open source code without reviewing it may introduce vulnerabilities, impacting users' data and privacy. * Plagiarism: Claiming open source code as original work, especially in academic or professional settings, is dishonest.

Question 62

What is a modifier?

Answer 62

A modifier is a keyword in programming used to change the properties or behavior of classes, methods, or variables. Common examples include: * public, private – control access (access modifiers) * static – indicates something belongs to the class, not instances * final – makes a variable constant or prevents method overriding

Question 63

Aggregation vs inheritance

Answer 63

Inheritance: is_a Aggregation: has_a

Question 64

What is the arrow type for: * uses (dependency) * has_a * is_a

Answer 64

uses: dashed arrow has_a: diamond arrow is_a: normal arrow

Question 65

Object reference

Answer 65

An object reference is a variable that holds the memory address of an object, not the actual object itself.

Question 66

Open source movement

Answer 66

The Open Source Movement is a social and technological shift focused on freely sharing software source code, so that anyone can view, modify, and distribute it.