The inner workings of the method/function are hidden from you. You're a software developer at an investment bank, and need to build a system that places orders into a market.When you call a method or function, you just need to know the parameters. There are a lot of great answers here, but I often find using BOTH interfaces and abstract classes is the best route. They can be a mean to restrain the way API contracts should be implemented. Abstract classes can implement private and protected methodsĪbstract classes should be used for (partial) implementation.An abstract class can implement an interface.Adding a new method to an abstract class has no ripple effect on extending classes.Modification of existing abstract class code has ripple effects on extending classes (implementation maintenance).An abstract class can define instance variables.An abstract class can define both static and instance constants (final).A class can extend at most one abstract class.In general, interfaces should be used to define contracts (what is to be achieved, not how to achieve it). An interface cannot extends or implement an abstract class.Adding a new method has ripple effects on implementing classes (design maintenance).An interface cannot define instance variables.An interface can only define public static final constants.An interface cannot provide any code at all.A class can implement multiple interfaces. You should either use abstract classes or work around this limitation with generics. (one is see is template method design pattern is conceptually based on Mentioned above where specifically we require to use abstract class Reiterating the question: there is any other scenario besides these The only drawback of doing that is calling methods via their interface name is slightly slower than calling them via their abstract class name. Implementors can ignore your abstract class if they choose. You can offer the best of both worlds, an interface and an abstract class. In Java, a class can inherit from only one base class. That may be highly inconvenient if the other programmers wanting to use your package have already developed their own class hierarchy independently. The catch is, code using it must use your class as the base. It usually defines some default implementations and provides some tools useful for a full implementation. You might not want to expose everything.Īn abstract class, in contrast, provides more structure. The disadvantage is every method in the interface must be public. To them, your interface is only incidental, something that have to add on to the their code to be able to use your package. Interfaces are better at providing common functionality for unrelated classes.Īn interface allows somebody to start from scratch to implement your interface or implement your interface in some other code whose original or primary purpose was quite different from your interface. You can’t go and change an Interface without having to change a lot of other things in your code, so the only way to avoid this would be to create a whole new Interface, which might not always be a good thing.Ībstract classes should primarily be used for objects that are closely related. Reiterating the question: Are there any other scenarios, besides those mentioned above, where specifically we require to use abstract class (one is see is template method design pattern is conceptually based on this only)?Ĭhoosing between these two really depends on what you want to do, but luckily for us, Erich Gamma can help us a bit.Īs always there is a trade-off, an interface gives you freedom with regard to the base class, an abstract class gives you the freedom to add new methods later. We can extend max of one abstract class, but can implement more than one interface Use interface if you need to put the signature to be same (and implementation different) so that you can comply with interface implementation Use abstract class when the requirement is such that we need to implement the same functionality in every subclass for a specific operation (implement the method) and different functionality for some other operations (only method signatures) I know the basic difference between abstract class and interface. I am sorry if I was not able to state the question clearly. Q: In which scenario it is more appropriate to extend an abstract class rather than implementing the interface(s)?Ī: If we are using template method design pattern. I was asked a question, I wanted to get my answer reviewed here.
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