[JAVA] Simply consider "why use interface"

It is to simplify the mounting and promote the componentization.

The interface is responsible for connecting or separating the chaotic ** real world ** from the strict ** computer world **. To make it easier to make parts, implementation is as simple as possible, and interface blocks complexity!

Reasons to allow multiple inheritance in interface and not in general classes

Since interface describes business ** specifications ** that are close to the chaotic real world, it replaces the complexity of implementation-level general classes by allowing multiple inheritance.

• Supplement ** Simplification **: By reducing the problem domain, the chain and spread of problems are limited, and the versatility as a part is improved. ** Allow multiple inheritance **: There are differences depending on the language, but if you respect the meaning of interface, you can voluntarily limit multiple inheritance by making the general class like interface in other languages as well. We believe that we will take advantage of the inherent benefits of object orientation.

bonus#

It is the designer who defines the relationships and conditions between the interfaces. The implementer simply codes according to the design without being aware of the complexity of the business. However, it is important to be careful not to bring implementation (processing) conditions into the interface. On the contrary, it is important to be careful not to bring (business) conditions between intefaces into the implementation (processing). To that end, the interface allows multiple inheritance to represent complexity, and the implementation limits multiple inheritance to prevent complexity.

In addition, the ** function ** that associates business and processing is both ** common language **.