Design patterns

 

Design that is more automated and require less maintenance is the standard.

Getters and setters:

Setters can be used for validation and constraining the value to be set to a particular range.

Getters can be used for returning default value, if the variable is not set yet or for lazy instantiation.


Can’t make objects out of abstract class. Abstract class can have some non abstract members.

Interface have only abstract methods.


 

Image result for design patterns java


Creational:

  1. Singleton:
    1. Can only have one instance of that particular class.
    2. President of a country, System in java.
    3. Private constructor, singleton using enum.
    4. @Singleton annotation.
    5. Difficult to unit test – why?
  2. Factory:
    1. Having a logic to return a particular subclass object, when asked for a class object.
  3. Abstract Factory:
  4. Builder:
    1. Separates object construction from its representation.
    2. interfaces.
  5. Prototype:
    1. Chess game initial setup.
    2. Copying/cloning the initial setup rather than creating the initial setup everytime you need it. Reduce redundant work.
    3. Copy a fully initialized instance.
    4. Link to code.

How to create objects?

Structural:

Inheritance? Interface? etc.

How are different classes related?

How are objects composed?

  1. Adapter:
    1.  Match interfaces of different classes. helps to communicate.
  2. Composite:
  3. Proxy:
    1. An object representing another object, like credit card as a proxy of bank account.
    2. Remote object and Home object(proxy).
  4. Flyweight:
    1. Reuse same objects by resetting values of the objects appropriately instead of creating new objects every time.
  5. Facade:
    1. Event managers, process, execute, group many steps into a single step.
  6. Bridge:
  7. Decorator:
    1. Add responsibilities to objects dynamically.
    2. Ex: adding different Toppings for different pizzas, adding discounts to different orders.

Behavioral:

Interactions between different objects.

  1. Template method:
  2. Mediator:
    1. instead of applications talking to each other, we use an enterprise service bus.
  3. Chain of responsibility:
    1. Passing a request through different objects.
  4. Observer:
    1. A way of notifying a change to a number of classes.
    2. This pattern is implemented in java.
    3. Subject extends Observable.
    4. Who wants to listen implements Observer and registers with the subject.
  5. Strategy:
    1. change the implementation/strategy of an interface at a later point in time.
    2. Pass whatever implementation needs to be used as an argument.
  6. Command:
    1. Encapsulate a command request as an object.
    2. java.lang.runnable threads are implemented like this.
  7. State:
  8. Visitor:
    1. Adding new operations to a particular class without inheritance and wi
  9. Iterator:
    1. Sequentially access the elements of a collection.
  10. Interpreter:
  11. Memento:
    1. Saving states of something as objects to restore them in future point of time if necessary.
    2. Undo/Redo operations.

Strategy pattern:

What:

 

Strategy design pattern.PNG

When:

Strategy pattern - when.PNG


Observer pattern:

when:

Observer pattern - when

What:

Observer pattern

Factory pattern :

Factory pattern - whenFactory pattern

Abstract Factory pattern:

Singleton pattern:

Singleton pattern.PNG

 Builder pattern:

Builder pattern.PNG

Prototype pattern:

 

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Dependency injection

dependency injection1.PNG

What is dependency injection?

Instead of initiating the object we are dependent on, we take help of a dependency framework which will push the ready made object to the dependent class during runtime.

In the above picture we are not initializing hotDrink with new hotDrink(), instead we are getting it as a constructor parameter.

Why is it useful?

This is useful to decouple two different code packages and remove direct dependency.

If you have an interface which can have multiple implementations, with the dependency injection framework, you can choose to run which implementation to run at runtime. Suppose you want to isolate and test a particular package, you can provide mock implementations of all other interfaces it is dependent on.

If you have to do the same without DI injection and interfaces, then you need to change code in lot of places, calling mock object at all the places you were calling original object to test.

It is useful when you have dependencies depending on other dependencies and so on.

Implementing with Google Guice:

Guice diGuice di2

You should usually initialize the injector where you bootstrap the program.

bind or guice configure() helps you define which implementation of interface to use.

@implementedby annotation can be used instead of configure() and bind.

@implementedby can be used as a default one.

If both guice module(bind) and @implementedby compete for different implementations of same interface, guice module wins.


 

Wanna have conditional logic to pick implementations?

Providers


Dependency injection without interface:

 

Dependency injection

Enable a class to be generic by making it disown the responsibility of defining an object in itself. Make other classes define the input object for it.

If you want to change the input object , you dont need to change the original class with dependency injection.

dependency injection

A spring container contains a set of objects or beans.

Essence of Rich Dad Poor Dad

Identify what are assets and what are liabilities.

Increase asset column.

Don’t work for money, make money work for you.

Rich buy luxuries late.

Rich guys income statement and balance sheet.

rdpd.jpg

How corporations help rich with taxes.

5oxAy.png

Corporations earn, spend and then pay taxes on the rest.

Individuals earn, get taxed and then spend.

Listing some assets:

  1. Businesses that do not require my presence.
  2. Stocks – Fortunes are made in new stock issues(new stocks are tax-free).
  3. Bonds.
  4. Income generating real estate.
  5. Notes (IOUs).
  6. Royalties from intellectual property.

Dimensions of financial literacy:

  1. Accounting:
  2. Investing:
  3. Understanding markets:
  4. The law: