SPSC Lecturer Computer Science (BPS-17) Interview Questions
The Sindh Public Service Commission asked the following questions during interviews for the position of Lecturer Computer Science (BPS-17) in the College Education Department of the Government of Sindh:
1- Difference between Object and Class
The difference between an object and a class in object-oriented programming (OOP) can be understood as follows:
Class
- A class is a blueprint or template that defines the properties (attributes) and behaviors (methods) that objects created from the class will have.
- It does not occupy any memory space until an object is created from it.
- It encapsulates data for the object and methods to manipulate that data.
- Example: A
Carclass might have attributes likecolor,make, andmodel, and methods likedrive()andbrake().
Object
- An object is an instance of a class. It is a concrete entity that occupies memory and has state and behavior defined by its class.
- Multiple objects can be created from the same class, each with its own unique state.
- Example:
myCar = Car()creates an objectmyCarof the classCar. This specific car might have the color red, be a Tesla, and be a Model S.
In summary, a class defines the structure and behavior of objects, while an object is an individual instance of a class with specific values for its attributes.
2- What is the difference between Cache and Register? Who is the fastest?
The difference between cache and register, along with their speed comparison, can be understood as follows:
Cache
- Location: Located between the main memory (RAM) and the CPU.
- Purpose: Stores copies of frequently accessed data from main memory to reduce the time it takes for the CPU to access this data.
- Size: Typically much larger than registers but smaller than main memory.
- Speed: Faster than main memory but slower than registers.
- Levels: Usually has multiple levels (L1, L2, L3) with L1 being the smallest and fastest and L3 being the largest and slowest.
- Usage: Used to store data and instructions that are frequently accessed, thereby improving the overall performance of the system.
Register
- Location: Located within the CPU.
- Purpose: Stores data and instructions that the CPU is currently processing.
- Size: Very small in size (typically a few bytes).
- Speed: The fastest type of memory in a computer system.
- Types: Includes different types such as data registers, address registers, and special-purpose registers (e.g., instruction register, accumulator).
- Usage: Used for immediate data manipulation and processing within the CPU.
Who is Fastest?
- Registers are the fastest type of memory, as they are directly accessible by the CPU and are designed to operate at the speed of the CPU clock. Cache memory, while very fast, is slightly slower than registers.
3- Difference between Inheritance and Polymorphism in OOP
The difference between inheritance and polymorphism in object-oriented programming (OOP) can be summarized as follows:
Inheritance
- Definition: Inheritance is a mechanism where a new class (called the subclass or derived class) is created from an existing class (called the superclass or base class). The new class inherits attributes and methods from the existing class.
- Purpose: It allows for code reuse and the creation of a hierarchical relationship between classes.
- Example: If you have a
Vehicleclass with properties likespeedand methods likemove(), you can create aCarclass that inherits fromVehicleand adds additional properties and methods specific to cars. - Usage: Commonly used to implement the “is-a” relationship. For instance, a
Caris aVehicle.
Polymorphism
- Definition: Polymorphism allows objects of different classes to be treated as objects of a common superclass. It enables a single interface to represent different underlying forms (data types).
- Purpose: It allows for flexibility and the ability to define one interface and have multiple implementations.
- Types:
- Compile-time (or static) polymorphism: Achieved through method overloading (same method name with different parameters) and operator overloading.
- Runtime (or dynamic) polymorphism: Achieved through method overriding (a subclass provides a specific implementation of a method that is already defined in its superclass).
- Example: If you have a
Shapeclass with a methoddraw(), you can have subclasses likeCircle,Square, andTriangleeach implementing thedraw()method differently. At runtime, you can calldraw()on an object of typeShape, and the appropriate subclass method will be executed. - Usage: Enables the “many forms” behavior. For example, you can write a function that operates on objects of type
Shapewithout needing to know the exact subclass.
In summary, inheritance establishes a hierarchical relationship between classes and facilitates code reuse, while polymorphism allows for one interface to be used for a general class of actions, promoting flexibility and integration.
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