Interface of java program

Note : With the release of Java 9, private methods are also supported in interfaces. We cannot create objects of an interface.

Hence, private methods are used as helper methods that provide support to other methods in interfaces. In the above program, we have created an interface named Polygon. It includes a default method getPerimeter and an abstract method getArea. We can calculate the perimeter of all polygons in the same manner so we implemented the body of getPerimeter in Polygon.

Now, all polygons that implement Polygon can use getPerimeter to calculate perimeter. However, the rule for calculating the area is different for different polygons. Hence, getArea is included without implementation. Any class that implements Polygon must provide an implementation of getArea. Course Index Explore Programiz.

Java for Loop. Arrays in Java. Interfaces in Java. Java ArrayList. Popular Examples Check prime number. Print the Fibonacci series. Print Pyramids and Patterns. Multiply two matrices. Find the standard deviation. Reference Materials String. Start Learning Java. Explore Java Examples.

Related Topics Java enum Inheritance and Interface. Java Collection Interface. Java ConcurrentMap Interface. Java Interface In this tutorial, we will learn about Java interfaces. Active 9 years, 9 months ago.

Viewed 28k times. Community Bot 1 1 1 silver badge. Add a comment. Active Oldest Votes. To put it simply, instead of writing your classes in a way that says I depend on this specific class to do my work you write it in a way that says I depend on any class that does this stuff to do my work. Eric King Eric King 11k 5 5 gold badges 41 41 silver badges 51 51 bronze badges. Not a good answer, unfortunately. It does not mean that you can't depend on a specific class to do the work. As a counter-example to your ILogger example, I offer for consideration the classes java.

Logger and org. Logger : both of these very popular logging APIs do not implement a separate interface, being used directly from client code. Client code which is still "programming to the interface", the interface of the Logger class. If you write code that depends specifically on org. Logger , you are not "programming to an interface". If you write code that doesn't care whether the logger provided is java. Logger or org. Logger or any other logger implementation that exposes the common interface, then you are programming to an interface.

EricKing But people do write code to the interface of Logger classes all the time. When they do that, they are programming to the interface; for sure, they are not programming to any implementation inside the class. I think you are confused about what an "interface" is. The java. Logger public class, like any other public class, has an implicit public interface, but an interface nonetheless, to which you can program to.

We are agreeing that if the code you write only knows about and cares about and depends on the interface , then we're golden.

It's depending on any specific class e. Logger' to do your work. EricKing Ok, we agree on what an interface is. About the principle of "program to an interface, not an implementation" from GoF , my interpretation is as explained in "Effective Java", 2ed. It is about the type you use for local variables, parameter types, and return types; it does not forbid instantiating an implementation class with new , nor does it mandate every class having a separate interface.

From the book: "It is entirely appropriate to refer to an object by a class rather than an interface if no appropriate interface exists. Show 3 more comments. Thomas Zoechling Thomas Zoechling This answer went inside my head : — Setu Kumar Basak. Nice explanation of interfaces themselves, but it doesn't really answer the question.

Polymorphism depends on programming to an interface, not an implementation. There are two benefits to manipulating objects solely in terms of the interface defined by abstract classes: Clients remain unaware of the specific types of objects they use, as long as the objects adhere to the interface that clients expect.

Clients remain unaware of the classes that implement these objects. Clients only know about the abstract class es defining the interface. Joe Phillips Joe Phillips Real-world examples are applenty. Bozho Bozho k gold badges silver badges bronze badges. Previous Prev. Next Continue. Home Testing Expand child menu Expand. SAP Expand child menu Expand. Web Expand child menu Expand. Must Learn Expand child menu Expand. Big Data Expand child menu Expand. Live Project Expand child menu Expand.

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