Java program to make shape as an interface and implement it

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java program to make shape as an interface and implement it

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Although, case-1 executes without error. If you observe there is same method getName in both interface and in abstract class, where in abstract class the method has the implementation.

When you try to implement, then it's mandatory for a class to override all the abstract methods of an interface and then we are trying to extend the abstract class which has already has an implementation for the method getName. There will a conflict for a child to call which method implementation as there will be two implementation for the same method getName. This is because of a specification in JLS. And there is a certain order of elements when you attempt to declare a class in Java:.

Or even worst, you might beed to declare Extends and Implements in order to use OR. There is a rule in java if want to implement an interface and extend a class we must extend a class first then we implement an interface. When the Java compiler turns a class into bytecode, it must first look to a parent class. That is because the underlying implementation of classes is to point to the bytecode of the parent class - which holds the relevant methods and fields.

Then it adds in pointers to the code of the child class functions - some of which are mandated by the 'implements' keyword. Because the parent class must be compilable, it is easier if the compiler knows up front what that class is. Further, you can extend only one class but implement any number of interfaces. The compilation time climbs if the extends keyword can be intermingled amongst any number of implements instructions. Compilers want to fail as fast as possible to decrease dev time, so this choice is logical.

Further, it helps you think clearly about the class for the same reason. You have to do like this. You can extends only one class but you can implement multiple interfaces by comma separately. Learn more.

Asked 7 years, 9 months ago. Active 25 days ago. Viewed 70k times. Ravi Ravi If anyone have doubts, they will ask, on the other hand, if other knows that answer, then post their answer instead of doing downvote. People are mis-using the down-vote features of SO. And, i really don't think so, it was really irrelevant question.

As, a beginner, many people don't about this. Active Oldest Votes. There have to be some rules. Why cant and be interchanged? Same reason.

If you found any supportive comments in JLS or any where. Please do share. For detail answer see. To avoid this conflict they made it mandatory to extend first and implement an interface later.Interface in java is one of the core concept. Java Interface is core part of java programming language and used a lot not only in JDK but also java design patterns. Most of the frameworks use java interface heavily. Interface in java provide a way to achieve abstraction.

Java interface is also used to define the contract for the subclasses to implement. Here we can create an interface Shape and define all the methods that different types of Shape objects will implement. For simplicity purpose, we can keep only two methods — draw to draw the shape and getArea that will return the area of the shape. Notice that Circle class has implemented all the methods defined in the interface and it has some of its own methods also like getRadius.

The interface implementations can have multiple type of constructors. Lets see another interface implementation for Shape interface.

Notice the use of override annotation, learn about annotations in java and why we should always use override annotation when overriding a method in java.

Although class typecasting has its own disadvantages. Thats all I have for interface in java. Since we use java interface a lot, we should be aware of its features.

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Make sure you use interfaces in designing the system and as a contract between the client and the subclasses implementing the interfaces. Update : Java 8 has changed the definition of interfaces with the introduction of default methods and static methods implementation. For more details, please read Java 8 interface. It creates ambiguity if we create an object for abstract class. Because we are not willing to use the methods of the abstract class. If we are not doing those methods so there is no point to create an object of the abstract class.

I dont understand interfaces! According to my understand using of interface is just to know the methods and variables that we are using in through out the code and instead of creating new variables again and again for same operation we can use declared variables under interface.

You have to implement all the unimplemented methods from all the interfaces. If you are using Eclipse IDE, it will show error there also. In java, an interface is a blueprint of a class.

It has provide only static constants and abstract methods in java. The interface is a mechanism to achieve fully abstraction. There can be only abstract methods in interface, not method body. An Interface is used to achieve fully abstraction and multiple inheritance in Java. Java Interface represents IS-A relationship.

Interface is also not be instantiated just like abstract class. By default, Interface fields are public, static and final and methods are public abstract in java.In Java, an interface defines a set of specifications that other classes must implement. For example.

Here, Polygon is an interface. We have used the interface keyword to declare an interface. The getArea method is a specification defined in the Polygon interface.

java program to make shape as an interface and implement it

All classes that use this interface must implement the getArea method. In the above example, we have created an interface Polygon. It includes a constant variable color and an abstract method getArea. It is important to note that, all methods inside an interface are implicitly public and all fields are implicitly public static final.

Hence, it's not necessary to specify the access specifier inside interfaces. For example, we can write the above code as. Like abstract classes, we cannot create objects of interfaces. However, we can implement interfaces in other classes. In Java, we use the implements keyword to implement interfaces.

Interface in Java

In the above program, we have created an interface Polygon. The Polygon interface has an abstract method getArea. This means that any class that implements Polygon must provide an implementation for the getArea method. Notice that, the Rectangle class which implements Polygon interface has the method getArea with implementation. In our above example, we have used getArea as a specification inside the interface Polygon. This is like setting a rule that, we should be able to get the area of every polygon.

So any class that implements the Polygon interface must provide an implementation for the getArea method. Similar to abstract classes, interfaces help us to achieve abstraction in Java.

Here, we know getArea calculates the area of polygons but the way area is calculated is different for different polygons. Hence, the implementation of getArea is independent of one another. Interfaces are also used to achieve multiple inheritance in Java. If a subclass is inherited from two or more classes, it's multiple inheritance.

In Java, multiple inheritance is not possible by extending classes. However, a class can implement multiple interfaces. This allows us to get the functionality of multiple inheritance in Java. Here, Rectangle has to provide an implementation for all methods of both Line and Polygon. Similar to a class, we can access static methods of an interface using its references.

Also, interfaces support private methods with the release of Java 9. Now you can use private methods and private static methods in interfaces. Since you cannot instantiate interfaces, private methods are used as helper methods that provide support to other methods in interfaces.

With the release of Java 8, methods with implementation default methods were introduced inside an interface.

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Before that, all the methods were abstract in Java. To declare default methods inside interfaces, we use the default keyword.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Code Review Stack Exchange is a question and answer site for peer programmer code reviews. It only takes a minute to sign up. To learn more about OOP, nhgrif challenged me to implement a Shape abstract class more details in code remarks below.

Here is how I did it. Any and all advice appreciated! I have a comment about the basic premise. The Shape should not be an abstract class, but an interface.

It has no concrete implementations for any methods, and making it an abstract class makes it hard to inherit from other places too. Consider this instead:.

java program to make shape as an interface and implement it

The pi field on your Circle class should be private. There's no need to re-expose an already public constant in another way. I would avoid the 'unit' default constructors. They don't help with anything. When would someone want to call new Triangle and not want to have the dimensions? Your classes are missing a toString method. These are useful for many reasons, especially debugging. You don't have a plan for out-of-bound dimensions. What will you do with negative, NaN, or infinite input?

A nitpick on names: The dimensions of a rectangle should be width and height not width and length. The constructor of Triangle should take descriptive parameter names, such as side1Length.

You have more excuse to use a and b for private fields especially in this short, pure math codebut single-character names are generally frowned upon. For extra credit, replace your main method with 3 unit tests 1 test class with 3 methods that can be easily run from the IDE. Though, there's no need for you to take up namespace or memory when you can directly use Math. For instance, your double area method's implementation could be:. I like that you use the abstract class to declare in your tests, doing that will afford you some flexibility in the future, just make sure you understand that when you rely on specific methods that only exist in a subclass you'd have to declare with that subclass.

In the comment you refer to the perimeter of the triangle, but in your code you don't use the actual perimeter. This is very small code duplication.An interface is a completely " abstract class " that is used to group related methods with empty bodies:.

To access the interface methods, the interface must be "implemented" kinda like inherited by another class with the implements keyword instead of extends. The body of the interface method is provided by the "implement" class:. However, it can be achieved with interfaces, because the class can implement multiple interfaces.

Note: To implement multiple interfaces, separate them with a comma see example below. If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:.

LOG IN. New User? Sign Up For Free! Forgot password? Notes on Interfaces: Like abstract classesinterfaces cannot be used to create objects in the example above, it is not possible to create an "Animal" object in the MyMainClass Interface methods do not have a body - the body is provided by the "implement" class On implementation of an interface, you must override all of its methods Interface methods are by default abstract and public Interface attributes are by default publicstatic and final An interface cannot contain a constructor as it cannot be used to create objects Why And When To Use Interfaces?

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Java Interfaces Crash Course (Implementing Comparable and Defining your own Interface)

W3Schools is Powered by W3.Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available. To declare a class that implements an interface, you include an implements clause in the class declaration. Your class can implement more than one interface, so the implements keyword is followed by a comma-separated list of the interfaces implemented by the class.

By convention, the implements clause follows the extends clause, if there is one. If you want to be able to compare the size of similar objects, no matter what they are, the class that instantiates them should implement Relatable. Any class can implement Relatable if there is some way to compare the relative "size" of objects instantiated from the class.

For strings, it could be number of characters; for books, it could be number of pages; for students, it could be weight; and so forth. For planar geometric objects, area would be a good choice see the RectanglePlus class that followswhile volume would work for three-dimensional geometric objects.

All such classes can implement the isLargerThan method. If you know that a class implements Relatablethen you know that you can compare the size of the objects instantiated from that class. Here is the Rectangle class that was presented in the Creating Objects section, rewritten to implement Relatable.

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Because RectanglePlus implements Relatablethe size of any two RectanglePlus objects can be compared. All rights reserved. Hide TOC. Interfaces and Inheritance. Multiple Inheritance of State, Implementation, and Type. A Sample Interface, Relatable Consider an interface that defines how to compare the size of objects.

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The line of code, shown in bold in the previous example, casts other to a RectanglePlus instance. Type casting tells the compiler what the object really is. Invoking getArea directly on the other instance other.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Create a Shape interface which has an area method which returns the area of the shape as a double.

Create classes Circle and Rectangle which implement the Shape interface. These classes have attributes which reflect their dimensions radius for a circle, height and width for a rectangle which are set by their constructors. Create a Drawable interface with setColour Color csetPosition int x, int yand draw Graphics g methods.

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Create the classes DrawableCircle and DrawableRectangle with appropriate constructors which extend Circle and Rectangle respectively and implement the Drawable interface.

Create a ShapesDriver class which extends Frame and has the main and paint Graphics g methods in it. Place into this array list a DrawableCircle and a DrawableRectangle where you have set the dimensions, position and colour. In the paint method iterate through the ArrayList and the invoke the draw method for each shape.

Learn more. Implementing a Shapes application using the following criteria - small project Ask Question. Asked 6 years, 11 months ago. Active 6 years, 11 months ago. Viewed 7k times. Here's where I've got to but I can't seem to get the drawable classes to work?

Java Interface

Color; import java. Paul Samsotha k 28 28 gold badges silver badges bronze badges. How to do the whole thing? Look at my answer. That should get you started.

Work on that.

java program to make shape as an interface and implement it

If you have problems, come back ask for help. Show you've tried. Active Oldest Votes. Paul Samsotha Paul Samsotha k 28 28 gold badges silver badges bronze badges. I've implemented the code above, but I have an error on the draw section of the drawableRectangle class? Does the error say you need to initialize your values? If yea, you should initialize x and y with 0 value. I would initialize all my class member variable with some dummy value.

You should declare x and y as int. In your drawable classes you should declare Color c as a class member, as well as x and y. Sign up or log in Sign up using Google.