Design Patterns

Question 1

What is a Design Pattern?

Answer 1

It is an organized way to present things or build things. Vocabulary for talking about things or building things. Separate the things that change and the things that don’t change. You are more efficient knowing this.

Question 2

Architectural “Macroscale” Patterns?

Answer 2

You look at the growth structure from far away. Model view controller is an example of this. Pipe & Filter is an example of this. Pump -> Filter -> Filter -> Pump. Filters change the data. Event-based like in javacsript. Layering are all examples.

Question 3

Gang of 4 Patterns?

Answer 3

Structural, Behavioral, and Creational.

23 Structural Design Patterns.

Question 4

What is technical debt?

Answer 4

When you know the right thing to do is too long and instead you do the quick dirty option. Technical debt accumulates and makes anti-patterns. Viscosity, Dryness, Immobility, Needless reputation.

Question 5

What is UML

Answer 5

Unified Modeling Language: notation for describing various artifacts in OOP systems.

Question 6

DO inheritances follow Single Responsibility Class?

Answer 6

Yes we only let one model do a specific things. Even though they inherit.

Question 7

What is Cohesion?

Answer 7

cohesion refers to the degree to which the elements of a module belong together. Thus, cohesion measures the strength of relationship between pieces of functionality within a given module. For example, in highly cohesive systems functionality is strongly related

Question 8

Why doesn’t it work in javascript to call a method with no parenthesis?

Answer 8

it would be an expression whose value is the function itself, rather than a call to the function. It is becuase javascript functions are first class functions.

Question 9

4 Categories of Maintenance?

Answer 9

1. Corrective Maintenance where you repair and fix bigs
2. Perfective Maintenance where you expand functionality
3. Adaptive where you cope with changing environment
4. Preventative where you improve the needs.

Question 10

What is Composition?

Answer 10

The owned objects are usually destroyed when the owning object is destroyed.

Question 11

What is aggregation?

Answer 11

Owned Object survives destruction of owning object.

Question 12

How do you structure University to Departments in UML Model?

Answer 12

University has many departments, Departments have one University.
The Departments can’t survive without university, so composition.

Question 13

What is the Single Responsibility Principle?

Answer 13

A class housed have one and only one reason to change. A sign is a data clump traveling with the calls to this class and a fix is to extract classes.

Question 14

What is Open/Closed Principle?

Answer 14

You should be able to extend the behavior of classes without modifying existing code on which other classes or apps depend on it.

Question 15

Difference between the Template Method Strategy & the Delegate Strategy?

Answer 15

Template Method is when the class has the basic game plan and then it is customized by delegating specific behaviors to the sub classes. In Decorator, each subclass provides functionality of its own, but delegate to the parent class for basic functionality.

Template - Class delegates behavior to descendants
Decorator - Subclass delegate behavior to parent.

Question 16

What is Liskov Substitution?

Answer 16

A method designed to work on an object of Type T should also work on a n object of subtype of T. Subclasses destructively override behavior of parent. Classic example is trying to make a square form rectangle.

Question 17

Why is Forward-able in the standard Ruby library provided as a module not a class?

Answer 17

It would be awkward.

Question 18

Difference Between Module and Class?

Answer 18

Module provides methods you can use across a number of classes. Class has its own methods.

Question 19

What is Dependency Injection Principle?

Answer 19

If two classes depend on each other but their implementations change, it would be better for them to both depend on a separate abstract interface that is “injected” between them. Instead of hardwiring a dependency into the source code, you just inject the right value at run time and in the mean time you have inputs in that class for those values.

Question 20

What is the Demeter Principle?

Answer 20

A method can call other methods in its own class, and methods on the classes of its own instance variables. It like having an attribute of a certain class as one of your attributes. You can call self.wallet.balance for your balance.