Many junior developers make the mistake of thinking of interfaces, abstract and concrete classes as slight variations of the same thing, and choose one of them purely on technical grounds: Do I need multiple inheritance? Do I need some place to put common methods? Do I need to bother with something other than just a concrete class? This is wrong, and hidden in these questions is the main problem: "I". When you write code for yourself, by yourself, you rarely think of other present or future developers working on or with your code. Show
Interfaces and abstract classes, although apparently similar from a technical point of view, have completely different meanings and purposes. Summary
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On the importance of hiding implementation detailsA concrete class does the actual work, in a very specific way. For example, an On the other hand, high level users of a list don't really care how it is actually implemented, and they should be insulated from these details. Let's imagine that Java didn't expose the An abstract class is in the middle between interfaces and concrete classes. It is supposed to help implementations share common or boring code. For example, APIs versus SPIsInterfaces are low-cohesion gateways between different parts of code. They allow libraries to exist and evolve without breaking every library user when something changes internally. It's called Application Programming Interface, not Application Programming Classes. On a smaller scale, they also allow multiple developers to collaborate successfully on large scale projects, by separating different modules through well documented interfaces. Abstract classes are high-cohesion helpers to be used when implementing an interface, assuming some level of implementation details. Alternatively, abstract classes are used for defining SPIs, Service Provider Interfaces. The difference between an API and an SPI is subtle, but important: for an API, the focus is on who uses it, and for an SPI the focus is on who implements it. Adding methods to an API is easy, all existing users of the API will still compile. Adding methods to an SPI is hard, since every service provider (concrete implementation) will have to implement the new methods. If interfaces are used to define an SPI, a provider will have to release a new version whenever the SPI contract changes. If abstract classes are used instead, new methods could either be defined in terms of existing abstract methods, or as empty A note on Java 8 and default methodsAlthough Java 8 introduced default methods for interfaces, which makes the line between interfaces and abstract classes even blurrier, this wasn't so that implementations can reuse code, but to make it easier to change interfaces that serve both as an API and as an SPI (or are wrongly used for defining SPIs instead of abstract classes). Which one to use?
A corollary: the other way around is often wrongly done: when using a thing, always try to use the most generic class/interface that you actually need. In other words, don't declare your variables as Which of the following differences between class and interface is correct?A class can inherit another class. An Interface cannot inherit a class. A class can be inherited by another class using the keyword 'extends'. An Interface can be inherited by a class using the keyword 'implements' and it can be inherited by another interface using the keyword 'extends'.
What is the main difference between class and interface?Differences between a Class and an Interface:
A class can be instantiated i.e, objects of a class can be created. An Interface cannot be instantiated i.e, objects cannot be created. Classes does not support multiple inheritance. Interface supports multiple inheritance.
Which of the following statement is correct about interface and class?Answer and Explanation: 1. The only true statement is C), All methods defined in an interface must be implemented when used by another class.
What is difference between interface and abstract class Mcq?An abstract class can contain static variables and methods. An interface contains only public static final variables.
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