It is ane of the frequently asked Java questions from beginners which struggles to acquire the concept behind an interface. The chief divergence betwixt a degree as well as an interface lies inwards their usage as well as capabilities. An interface is the purest cast of abstraction available inwards Java where y'all only define the API or contract e.g. y'all define run() method on the Runnable interface without worrying most how something volition run, that is left to the implementor which volition exercise a degree to define how just to run. So an interface gives y'all method cite but how the demeanor of that method is come upward from the degree which implements it. That's your full general divergence betwixt an interface as well as degree inwards Java as well as applicable to all object oriented programming language, non only Java. Even though this inquiry is non just the difference betwixt abstract degree as well as interface, it's somewhat related to it because an abstract degree is cypher but a degree alongside unopen to abstract method. The points I convey discussed there, besides applicable hither inwards damage of rules of Java programming related to degree as well as interface.
1) Purpose
The interface is best suited for defining type because it promotes multiple inheritances inwards Java. It is fifty-fifty recommended past times Joshua Bloch inwards Effective Java. Since an interface tin extend multiple interfaces as well as a degree tin implement multiple interfaces, it all of a abrupt becomes to a greater extent than polymorphic. On the other hand, a degree is best suited for writing concrete code which does the actual job.
2) Instantiation
Since an interface is completely abstract y'all cannot exercise an object of them but a degree tin last both abstract as well as concrete thus y'all tin exercise an object of a concrete degree inwards Java.
For example
where Task is a degree which implements Runnable interface.
3) State
An interface tin define constants but that is non component of the pose down of an object, which is entirely defined past times the event variable. You cannot define pose down variable within interface inwards Java until JDK seven but that is changed straight off inwards Java SE 8, where y'all tin define both static as well as default methods within interface. (see Java SE 8 for Really Impatient past times Cay S. Horstmann to larn to a greater extent than most static as well as default methods)
4) Inheritance
H5N1 degree tin entirely inherit ane degree but an interface tin extend multiple interfaces. Similarly, a degree tin implement multiple interfaces but an interface cannot extend a class. This mightiness look confusing to y'all but Java allow multiple inheritance inwards cast of ane interface extending multiple interface but doesn't allow C++ means multiple inheritance where a degree tin extend multiple classes.
5) Flexibility
Interface adds flexibility inwards coding. Any code which is written using interface are to a greater extent than adaptable to a alter than code written using concrete classes. This is besides a pop object oriented pattern principle, normally known every bit "programming for interfaces than implementation". You tin come across my transportation service 10 object oriented pattern principles which every Java developer should know to larn to a greater extent than most that.
6) UML Diagram
In UML diagram an interface is represented using keyword <<interface>> spell degree doesn't demand anyword. Any degree which impelments interface is besides denoted via dotted describe alongside arrowhead every bit shown inwards next diagram. In this diagram y'all convey a degree called Circle which implements an interface called GeometricObject. There is unopen to other degree called ResizableCircle which extends Circle class as well as implement unopen to other interface called Resizable. If y'all are non really familiar alongside UML than y'all should read UML for Java Programmers past times Uncle Bob to larn to a greater extent than most UML inwards Java)
Difference betwixt degree as well as interface inwards Java
Now, let's test both syntactical as well as functional divergence betwixt a degree as well as interface inwards Java request past times point, this volition give y'all a meliorate thought of both of them.1) Purpose
The interface is best suited for defining type because it promotes multiple inheritances inwards Java. It is fifty-fifty recommended past times Joshua Bloch inwards Effective Java. Since an interface tin extend multiple interfaces as well as a degree tin implement multiple interfaces, it all of a abrupt becomes to a greater extent than polymorphic. On the other hand, a degree is best suited for writing concrete code which does the actual job.
2) Instantiation
Since an interface is completely abstract y'all cannot exercise an object of them but a degree tin last both abstract as well as concrete thus y'all tin exercise an object of a concrete degree inwards Java.
For example
Runnable r = new Runnable(); // compiler fault but Runnable r = new Task();; // Ok
where Task is a degree which implements Runnable interface.
3) State
An interface tin define constants but that is non component of the pose down of an object, which is entirely defined past times the event variable. You cannot define pose down variable within interface inwards Java until JDK seven but that is changed straight off inwards Java SE 8, where y'all tin define both static as well as default methods within interface. (see Java SE 8 for Really Impatient past times Cay S. Horstmann to larn to a greater extent than most static as well as default methods)
4) Inheritance
H5N1 degree tin entirely inherit ane degree but an interface tin extend multiple interfaces. Similarly, a degree tin implement multiple interfaces but an interface cannot extend a class. This mightiness look confusing to y'all but Java allow multiple inheritance inwards cast of ane interface extending multiple interface but doesn't allow C++ means multiple inheritance where a degree tin extend multiple classes.
5) Flexibility
Interface adds flexibility inwards coding. Any code which is written using interface are to a greater extent than adaptable to a alter than code written using concrete classes. This is besides a pop object oriented pattern principle, normally known every bit "programming for interfaces than implementation". You tin come across my transportation service 10 object oriented pattern principles which every Java developer should know to larn to a greater extent than most that.
6) UML Diagram
In UML diagram an interface is represented using keyword <<interface>> spell degree doesn't demand anyword. Any degree which impelments interface is besides denoted via dotted describe alongside arrowhead every bit shown inwards next diagram. In this diagram y'all convey a degree called Circle which implements an interface called GeometricObject. There is unopen to other degree called ResizableCircle which extends Circle class as well as implement unopen to other interface called Resizable. If y'all are non really familiar alongside UML than y'all should read UML for Java Programmers past times Uncle Bob to larn to a greater extent than most UML inwards Java)
Inheritance as well as Polymorphism which comes past times using interface.
That's all most the difference betwixt a degree as well as interface inwards Java. The most of import divergence is to sympathise when to exercise a degree as well as interface. As I convey previously explained on actual exercise of interface inwards Java, it permit y'all write polymorphic code which adds flexibility to your software. This is besides known every bit "programming for interfaces" inwards the object-oriented world.
Related Java as well as OOP tutorials y'all may like:
Further Learning
SOLID Principles of Object Oriented Design
Absolute Introduction to Object Oriented Programming inwards Java
Java - Object Oriented Programming [For Absolute Beginners]
That's all most the difference betwixt a degree as well as interface inwards Java. The most of import divergence is to sympathise when to exercise a degree as well as interface. As I convey previously explained on actual exercise of interface inwards Java, it permit y'all write polymorphic code which adds flexibility to your software. This is besides known every bit "programming for interfaces" inwards the object-oriented world.
Related Java as well as OOP tutorials y'all may like:
- Difference betwixt abstraction as well as encapsulation inwards Java? (answer)
- 30 OOP questions from Java Interviews alongside answrs (list)
- Why abstract degree is of import inwards Java? (answer)
- 21 Java Inheritance Interview Questions alongside answers (list)
- Differnece betwixt abstraction as well as polymorphism inwards Java? (answer)
- Can nosotros declare constructor within abstract degree inwards Java? (answer)
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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