2020 New Java Interview Questions-Design Patterns

What is the difference between a simple factory and an abstract factory?

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Simple factory pattern:

This pattern itself is very simple And it is used when the business is relatively simple. Generally used for small projects or situations where specific products are rarely extended (so that the factory class does not need to be changed frequently).

It consists of three roles:

• Factory role: This is the core of this model, containing certain business logic and judgment logic , according to different logic, specific factory products are generated. Such as the Driver class in the example.

• Abstract product role: It is generally the parent class inherited by a specific product or the interface implemented. Implemented by interface or abstract class. Such as the Car interface in the example.

• Specific product role: The object created by the factory class is an instance of this role. It is implemented by a concrete class in java, such as the Benz and BMW classes in the example.

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Use class diagrams to clearly represent the relationship between them ：

Abstract Factory Pattern:

First let’s understand what a product family is: It is located in different product hierarchical structures and has related functions. A family of connected products.

The BmwCar and BenzCar in the picture are two product trees (product hierarchy); and the BenzSportsCar and BmwSportsCar shown in the picture are one product family. They can all be put into the sports car family, so the functions are related. In the same way, BmwBussinessCar and BenzBusinessCar are also a product family.

It can be said that the difference between it and the factory method pattern lies in the complexity of creating objects. Moreover, the abstract factory pattern is the most abstract and general among the three. The purpose of the abstract factory pattern is to provide an interface for the client to create product objects in multiple product families.

Moreover, the following conditions must be met to use the abstract factory pattern:

1. There are multiple product families in the system, and the system can only consume one family of products at a time

2. Products belonging to the same product family should be used accordingly.

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Let’s take a look at the various roles of the abstract factory pattern (the same as the factory method):

• Abstract Factory Role: This is the core of the factory method pattern and it has nothing to do with the application. It is the interface that a specific factory role must implement or the parent class that must be inherited. In java it is implemented by abstract classes or interfaces.

• Specific factory role: It contains code related to specific business logic. Called by an application to create an object corresponding to a specific product. In java it is implemented by concrete classes.

• Abstract product role: It is the parent class inherited by a specific product or the interface implemented. In Java, there are generally abstract classes or interfaces to implement.

• Specific product role: The object created by the specific factory role is an instance of this role. It is implemented by specific classes in java.

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