SSD - 1. Programming Paradigms

Question 1

What is a class?

Answer 1

A class is a blueprint that sets out what data the object can use (its instance variables) and what it can do (its methods)

Question 2

What are instance variables?

Answer 2

These are the variables that the object can use once created

Question 3

What are methods?

Answer 3

Methods are the instructions that tell the object what it can do and how it can change the data in instance variables. Methods are defined in the class that was used to create the object. Methods can be function methods (always return one value) or procedure methods (may or may not return a value).

Question 4

What is an object?

Answer 4

An object is an instance of a class and it inherits the methods and instance variables of that class

Question 5

What is instantiation?

Answer 5

Instantiation is the process of creating an object from a class

Question 6

What is inheritance?

Answer 6

This is when a new object receives the instance variables and methods that were defined in the class

Question 7

What is encapsulation?

Answer 7

Encapsulation is the idea that objects are closed systems and their instance variables and methods cannot be modified from the outside

Question 8

What are messages?

Answer 8

Messages are how objects tell other objects to perform a task such as run. They are also used to pass data between objects

Question 9

What is concurrent programming?

Answer 9

Concurrent programming is allowing various processes to share access to the processors at the same time

Question 10

What is a thread?

Answer 10

A thread is a task or a process that needs access to resources (a sequence of instructions)

Question 11

What can streams sometimes do (negative)?

Answer 11

Streams can sometimes communicate and interfere with each other

Question 12

What can streams do?

Answer 12

Streams of threads can run concurrently, maximising the use of processors. A stream is a set of threads that need to run at the same time.

Question 13

What are the advantages of threads?

Answer 13

1. Tasks can run while users are interacting with applications
2. Tasks that take a long time to run will not delay tasks that only need a short time to run
3. complex programs can make better use of multiple resources in new multi-core processor architectures

Question 14

What problems are there with multi-threaded programs?

Answer 14

1. Deadlock - Two threads competing for processor time, each waiting for the other to finish. Both in a waiting state.
2. Race condition - Two threads may need access or alter the same variable. A system needs to lock threads from accessing the same variable
3. Resource starvation - A thread accesses resources, locking out lower priority threads. Lower priority threads do not get access. Thread scheduling needs to ensure that all threads get access to necessary resources

Question 15

What is concurrency control?

Answer 15

Concurrency control is a system that coordinates the interactions between threads so that they are all correctly scheduled and resources are shared among operations based on the priority assigned to a thread