Java interfaces

Java interfaces

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  JAVA - INTERFACES ElizabethAlexander Hindustan University
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  INTERFACES ● It isa collection of abstract methods. ● A class implements an interface, thereby inheriting the abstract methods of the interface. ● Along with abstract methods, an interface may also contain constants, default methods, static methods, and nested types. Method bodies exist only for default methods and static methods. ● Writing an interface is similar to writing a class. But a class describes the attributes and behaviors of an object. And an interface contains behaviors that a class implements. ● Unless the class that implements the interface is abstract, all the methods of the interface need to be defined in the class.
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  DIFFERENCE BETWEEN CLASSAND INTERFACE ● You cannot instantiate an interface. ● An interface does not contain any constructors. ● All of the methods in an interface are abstract. ● An interface cannot contain instance fields. The only fields that can appear in an interface must be declared both static and final. ● An interface is not extended by a class; it is implemented by a class. ● An interface can extend multiple interfaces.
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  Internal addition bycompiler •The java compiler adds public and abstract keywords before the interface method. More, it adds public, static and final keywords before data members.
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  Declaring Interfaces ● Theinterface keyword is used to declare an interface. Here is a simple example to declare an interface ■ public interface NameOfInterface { // Any number of final, static fields // Any number of abstract method declarations } Properties of Interfaces ● An interface is implicitly abstract. You do not need to use the abstract keyword while declaring an interface. ● Each method in an interface is also implicitly abstract, so the abstract keyword is not needed. ● Methods in an interface are implicitly public.
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  Example interface Animal { publicvoid eat(); public void travel(); } Implementing Interfaces ● A class uses the implements keyword to implement an interface. The implements keyword appears in the class declaration following the extends portion of the declaration.
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  DIFFERENCE BETWEEN ABSTRACTAND FINAL ● Simply, abstract class achieves partial abstraction (0 to 100%) whereas interface achieves fully abstraction (100%).