Abstract Class And Interface In Java Pdf Notes

abstract class and interface in java pdf notes

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Abstraction in JAVA shows only the essential attributes and hides unnecessary details of the object from the user.

In this tutorial, we will learn about abstract class and methods in Java along with understanding how we can implement abstraction using abstract classes. We will also have some code examples. A class which is declared using abstract keyword known as abstract class.

Java Interface

Abstraction in JAVA shows only the essential attributes and hides unnecessary details of the object from the user. In Java, abstraction is accomplished using Abstract class, Abstract methods, and Interfaces. Abstraction helps in reducing programming complexity and effort. In this tutorial, you will learn- What is Abstract Class? What are Abstract Methods? These classes can have abstract methods as well as concrete methods.

A normal class cannot have abstract methods. An abstract class is a class that contains at least one abstract method. We can understand the concept by the shape example in java. Consider the following class hierarchy consisting of a Shape class which is inherited by three classes Rectangle, Circle, and Triangle. The Shape class is created to save on common attributes and methods shared by the three classes Rectangle, Circle, and Triangle.

Shape Abstraction Example Now, assume you write code to create objects for the classes depicted above. Let's observe how these objects will look in a practical world.

An object of the class rectangle will give a rectangle, a shape we so commonly observed in everyday life.

An object of the class triangle will give a triangle, again a common everyday shape. But what would an object of Class Shape look like in a practical world??

If you observe the Shape class serves in our goal of achieving inheritance and polymorphism. But it was not built to be instantiated. Such classes can be labelled Abstract. An abstract java class cannot be instantiated. But such object will have no use in your code and will open a room for potential errors. Hence this is not desirable. A method without a body is known as an Abstract Method.

It must be declared in an abstract class. The abstract method will never be final because the abstract class must implement all the abstract methods.

The calculateArea method will have to be overridden by the inheriting classes. It makes no sense defining it in the Shape class, but we need to make sure that all the inheriting classes do have the method. Such methods can be labeled abstract. Syntax: abstract public void calculateArea ; For an abstract method, no implementation is required. Only the signature of the method is defined. Final Keyword in Java The final modifier applies to classes, methods, and variables.

The meaning of final varies from context to context, but the essential idea is the same. A final class cannot be inherited A final variable becomes a constant and its value cannot be changed. A final method cannot be overridden. This is done for security reasons, and these methods are used for optimization.

The abstract method is not implemented int the class Rectangle. To fix the issue uncomment line Step 4 Uncomment line The opposite cannot be true. This means that an abstract class does not necessarily have an abstract method. If a regular class extends an abstract class, then that class must implement all the abstract methods of the abstract parent. Java has had several advanced usage application including working with complex calculations in What is Quick Sort? Quick Sort algorithm follows Divide and Conquer approach.

It divides elements What is Command Line Argument in Java? Command Line Argument in Java is the information that is Home Testing. Must Learn! Big Data. Live Projects. What is Abstraction in Java? What is Abstract Class? What is Palindrome Number? A Palindrome Number is a number that even when reversed is same as What is a Variable in Java? Variable in Java is a data container that stores the data values

Interface (Java)

An interface in the Java programming language is an abstract type that is used to specify a behavior that classes must implement. They are similar to protocols. Interfaces are declared using the interface keyword , and may only contain method signature and constant declarations variable declarations that are declared to be both static and final. All methods of an Interface do not contain implementation method bodies as of all versions below Java 8. Starting with Java 8, default and static methods may have implementation in the interface definition. At present, a Java interface can have up to six different types. Interfaces cannot be instantiated , but rather are implemented.

Interface (Java)

A class which is declared with the abstract keyword is known as an abstract class in Java. It can have abstract and non-abstract methods method with the body. Abstraction is a process of hiding the implementation details and showing only functionality to the user. Another way, it shows only essential things to the user and hides the internal details, for example, sending SMS where you type the text and send the message. You don't know the internal processing about the message delivery.

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When to use abstract classes: To implement the same or different behaviour among multiple related objects. Abstract classes create "is a" relations while interfaces provide "has a" capability. Animal is an abstract class with shared attributes: name and lifeExpectancy and abstract methods: remember and protectOwner. Dog and Cat are Animals that have implemented the remember and protectOwner methods. Cat can climb but Dog cannot. Dog can think but Cat cannot.

In this tutorial, we will learn about Java interfaces.

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Беккер с трудом вел мотоцикл по крутым изломам улочки. Урчащий мотор шумным эхо отражался от стен, и он понимал, что это с головой выдает его в предутренней тишине квартала Санта-Крус. В данный момент у него только одно преимущество - скорость. Я должен поскорее выбраться отсюда.

Когда он наконец заговорил, голос его звучал подчеркнуто ровно, хотя было очевидно, что это давалось ему нелегко. - Увы, - тихо сказал Стратмор, - оказалось, что директор в Южной Америке на встрече с президентом Колумбии. Поскольку, находясь там, он ничего не смог бы предпринять, у меня оставалось два варианта: попросить его прервать визит и вернуться в Вашингтон или попытаться разрешить эту ситуацию самому. Воцарилась тишина. Наконец Стратмор поднял усталые глаза на Сьюзан.

Java Abstract class and methods