An interface inwards Java has remained a complex theme for many beginners to understand. The commencement matter which puzzles many programmers is the fact that you cannot define whatever method within interface, it a only declaration. By rule, all method within interface must move abstract (Well, this dominion is changing inwards Java 8 to let lambda expressions, directly interface tin forcefulness out bring ane non-abstract method, also known every bit a default method). So, if you lot can't define anything, Why nosotros ask an interface? what's the purpose of an interface, if nosotros are anyway going to write a shape too override them to provide behaviour, Can't nosotros declare those methods within the shape itself without using interface etc. Well, if you lot are thinking inwards price of demeanour too therefore you lot are actually missing the betoken of interface.
I recall ane has to read Effective Java, to empathise best purpose of interface. Interface is neat to declare Type, they promote code reusability, too they are the existent driver of polymorphism inwards Java.
Interface also allows multiple inheritance inwards Java, which makes it possible for a shape to pop off Canvas, every bit good every bit EventListener, which is used to describe graphics every bit good every bit to to procedure events.
In this post, I volition percentage few points, which volition aid you lot to empathise what is the actual purpose of interface inwards Java. By the way, if you lot are confused betwixt abstract shape too interface, too therefore you lot may desire to read my previous ship service on difference betwixt interface too abstract shape inwards Java.
There are several reasons, an application developer needs an interface, ane of them is Java's characteristic to provide multiple inheritance at interface level. It allows you lot to write flexible code, which tin forcefulness out adjust to grip time to come requirements. Some of the concrete reasons, why you lot ask interface is :
1) If you lot solely implement methods inwards subclasses, the callers volition non move able to telephone telephone them via the interface (not mutual betoken where they are defined).
2) Java 8 volition innovate default implementation of methods within the interface, but that should move used every bit exception rather than rule. Even Java designer used inwards that way, it was introduced to keep backward compatibility along amongst supporting lambda expression. All evolution of Stream API was possible due to this change.
3) Interfaces are a means to declare a contract for implementing classes to fulfil; it's the primary tool to create abstraction too decoupled designs betwixt consumers too producers.
4) Because of multiple inheritance, interface allows you lot to care for ane matter differently. For representative a shape tin forcefulness out move treated every bit Canvas during drawing too EventListener during consequence processing. Without interface, it's non possible for a shape to bear similar ii unlike entity at ii unlike situations. Here is an representative of how interface supports multiple inheritance inwards Java
5) Interface are primal of API design. In fact smaller interface similar Comparable, Runnable, Callable makes heart of Java API. Though neat attention is required spell designing too publishing interface, because ane time published, you lot tin forcefulness out non alter interface without breaking upwards all your clients, i.e. classes which bring implemented your interface. On extreme case, from Java 8 onwards, you lot tin forcefulness out purpose default method to rescue, but every bit I said, it should move exception than rule.
6) "Programming to interface than implementation" is ane of the popular Object oriented pattern principle, too purpose of interface promotes this. H5N1 code written on interface is much to a greater extent than flexible than the ane which is written on implementation.
7) Use of interface allows you lot to render a novel implementation, which could move to a greater extent than robust, to a greater extent than functioning inwards after phase of your development.
In short principal purpose of interface is to facilitate polymorphism. interface allows a shape to bear similar multiple types, which is non possible without multiple inheritance of class. It also ensures that you lot follow programming to interface than implementation pattern, which eventually adds lot of flexibility inwards your system.
I recall ane has to read Effective Java, to empathise best purpose of interface. Interface is neat to declare Type, they promote code reusability, too they are the existent driver of polymorphism inwards Java.
Interface also allows multiple inheritance inwards Java, which makes it possible for a shape to pop off Canvas, every bit good every bit EventListener, which is used to describe graphics every bit good every bit to to procedure events.
In this post, I volition percentage few points, which volition aid you lot to empathise what is the actual purpose of interface inwards Java. By the way, if you lot are confused betwixt abstract shape too interface, too therefore you lot may desire to read my previous ship service on difference betwixt interface too abstract shape inwards Java.
Why nosotros ask Interface inwards Java
1) If you lot solely implement methods inwards subclasses, the callers volition non move able to telephone telephone them via the interface (not mutual betoken where they are defined).
2) Java 8 volition innovate default implementation of methods within the interface, but that should move used every bit exception rather than rule. Even Java designer used inwards that way, it was introduced to keep backward compatibility along amongst supporting lambda expression. All evolution of Stream API was possible due to this change.
3) Interfaces are a means to declare a contract for implementing classes to fulfil; it's the primary tool to create abstraction too decoupled designs betwixt consumers too producers.
4) Because of multiple inheritance, interface allows you lot to care for ane matter differently. For representative a shape tin forcefulness out move treated every bit Canvas during drawing too EventListener during consequence processing. Without interface, it's non possible for a shape to bear similar ii unlike entity at ii unlike situations. Here is an representative of how interface supports multiple inheritance inwards Java
interface Canvas{ public void paint(Graphics g); } interface EventListener{ public boolean process(Event e); } pubic class Game implements Canvas, EventListener{ @Override public void paint(Graphics g){ g.drawLine(Color.RED); } @Override public boolean process(Event e){ KeyCode code = e.getKeyPressed().getCode(); } }
5) Interface are primal of API design. In fact smaller interface similar Comparable, Runnable, Callable makes heart of Java API. Though neat attention is required spell designing too publishing interface, because ane time published, you lot tin forcefulness out non alter interface without breaking upwards all your clients, i.e. classes which bring implemented your interface. On extreme case, from Java 8 onwards, you lot tin forcefulness out purpose default method to rescue, but every bit I said, it should move exception than rule.
6) "Programming to interface than implementation" is ane of the popular Object oriented pattern principle, too purpose of interface promotes this. H5N1 code written on interface is much to a greater extent than flexible than the ane which is written on implementation.
7) Use of interface allows you lot to render a novel implementation, which could move to a greater extent than robust, to a greater extent than functioning inwards after phase of your development.
In short principal purpose of interface is to facilitate polymorphism. interface allows a shape to bear similar multiple types, which is non possible without multiple inheritance of class. It also ensures that you lot follow programming to interface than implementation pattern, which eventually adds lot of flexibility inwards your system.
Further Learning
SOLID Principles of Object Oriented Design
Absolute Introduction to Object Oriented Programming inwards Java
Java - Object Oriented Programming [For Absolute Beginners]
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