My making your class as implementing Externalizable interface, you have to implement the contract for below methods void writeExternal(ObjectOutput out) Take an example of custom serialization of object. An interface does not have an implementation for a method is no longer valid now.ĭefine a contract and it has to be implemented by its implementer. Java 8 has reduced the gap between interface and abstract classes to some extent by providing a default method feature. If you are looking for Java as programming language, here are a few more updates: interface provides "has a" capability for classes. many unrelated objects can implement Serializable OR Externalizable interface.Ībstract class establishes "is a" relation with concrete classes. Establish relation among unrelated classes.Supports non-static / non-final fields.Code and members can be shared among related classes.Oracle documentation page provides general guidelines for the same. Interface: To implement a contract by multiple unrelated objectsĪbstract class: To implement the same or different behavior among multiple related objects I don't want to highlight the differences, which have been already said in many answers ( regarding public static final modifiers for variables in interface & support for protected, private methods in abstract classes) ![]() An interface definition consists of signatures of public members, without any implementing code. A more common definition is: An interface defines a contract that implementing classes must fulfill. This is because interfaces cannot define any implementation.Ī child class can only extend a single class (abstract or concrete), whereas an interface can extend or a class can implement multiple other interfaces.Ī child class can define abstract methods with the same or less restrictive visibility, whereas a class implementing an interface must define the methods with the exact same visibility (public).Īnyway I find this explanation of interfaces somewhat confusing. Similarly, an interface extending another interface is not responsible for implementing methods from the parent interface. ![]() When inheriting an abstract class, a concrete child class must define the abstract methods, whereas an abstract class can extend another abstract class and abstract methods from the parent class don't have to be defined. Methods and members of an abstract class can be defined with any visibility, whereas all methods of an interface must be defined as public (they are defined public by default). The key technical differences between an abstract class and an interface are:Ībstract classes can have constants, members, method stubs (methods without a body) and defined methods, whereas interfaces can only have constants and methods stubs. And interfaces are more related to duck typing in this language and it's a mix between conventions and special methods that call descriptors (the _method_ methods).Īs usual with programming, there is theory, practice, and practice in another language :-) In Python, abstract classes are more a programming trick you can get from the ABC module and is actually using metaclasses, and therefore classes. In Java, this rule is strongly enforced, while in PHP, interfaces are abstract classes with no method declared. Sometimes, they are not even what you think they are. While abstract classes and interfaces are supposed to be different concepts, the implementations make that statement sometimes untrue. My teammate complies and writes vehicle looking that way That can be very different, force them to provide their They ALL have fuel, so lets implement this for everybody. It's more about a person saying, " these classes should look like that, and they have that in common, so fill in the blanks!".įor example: // I say all motor vehicles should look like this: They are more expensive to use, because there is a look-up to do when you inherit from them.Ībstract classes look a lot like interfaces, but they have something more: You can define a behavior for them. It's great when it matters, such as in embedded devices.Ībstract classes, unlike interfaces, are classes. Implementing an interface consumes very little CPU, because it's not a class, just a bunch of names, and therefore there isn't any expensive look-up to do. My team mate complies and writes vehicle looking that way ![]() ![]() It's just a pattern.įor example (pseudo code): // I say all motor vehicles should look like this: There are only the signatures of the methods, which implies that the methods do not have a body. An interface is a contract: The person writing the interface says, " hey, I accept things looking that way", and the person using the interface says " OK, the class I write looks that way".Īn interface is an empty shell.
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