Any class which implements an interface is also denoted via a dotted line with an arrowhead as shown in the following diagram.One of the most well-liked and often-used platforms and programming languages is Java. In the UML diagram, an interface is represented using keyword > while the class doesn't need any words. You can also see my post on 10 object-oriented design principles which every Java developer should know to learn more about that. This is also a popular object-oriented design principle, commonly known as 'programming for interfaces than implementation'.

Any code which is written using an interface is more adaptable to a change than code written using concrete classes. FlexibilityThe interface adds flexibility to coding. This might seem confusing to you but Java allows multiple inheritances in form of one interface extending multiple interfaces but doesn't allow C++ style multiple inheritances where a class can extend multiple classes.ĥ. Similarly, a class can implement multiple interfaces but an interface cannot extend a class. (see these free Java 8 tutorials to learn more about static and default methods)Ī class can only inherit one class but an interface can extend multiple interfaces. You cannot define state variable inside interface in Java until JDK 7 but that is changed now in Java SE 8, where you can define both static and default methods inside interface. Where Task is a class that implements a Runnable interface.Īn interface can define constants but that is not part of the state of an object, which is only defined by the instance variable. Runnable r = new Runnable() // compiler error Since an interface is completely abstract you cannot create an object of them but a class can be both abstract and concrete hence you can create an object of a concrete class in Java. On the other hand, a class is best suited for writing concrete code which does the actual job. Since an interface can extend multiple interfaces and a class can implement multiple interfaces, it suddenly becomes more polymorphic. It is even recommended by Joshua Bloch in Effective Java. The interface is best suited for defining type because it promotes multiple inheritances in Java.

Now, let's examine both syntactical and functional differences between a class and interface in Java point by point, this will give you a better idea of both of them. The points I have discussed there, also applicable here in terms of rules of Java programming related to class and interface.ĭifference between class vs interface in Java and OOP Even though this question is not exactly the difference between abstract class and interface, it's somewhat related to it because an abstract class is nothing but a class with some abstract method. That's your general difference between an interface and class in Java and applicable to all object-oriented programming languages, not just Java. So an interface gives you a method name but how the behavior of that method has come from the class which implements it. you define run() method on the Runnable interface without worrying about how something will run, that is left to the implementor which will use a class to define how exactly to run. An interface is the purest form of abstraction available in Java where you just define the API or contract e.g. The main difference between a class and an interface lies in their usage and capabilities. It is one of the frequently asked Java questions from beginners who struggle to get the concept behind an interface.

Java interface programming example