To create an abstract class, just use the abstract keyword before the class keyword, in the class declaration. The idea behind inheritance in Java is that you can create new classes that are built upon existing classes. It is an important part of OOPs (Object Oriented programming system). This section provides you an example of the abstract class. Inheritance in Java is a mechanism in which one object acquires all the properties and behaviors of a parent object. If you inherit an abstract class, you have to provide implementations to all the abstract methods in it. With inheritance, you derive a new class based on an existing class, with modifications or extensions. With composition (aka aggregation ), you define a new class, which is composed of existing classes. There are two ways to reuse existing classes, namely, composition and inheritance. To use an abstract class, you have to inherit it from another class, provide implementations to the abstract methods in it. OOP - Composition, Inheritance & Polymorphism. If a class is declared abstract, it cannot be instantiated. Narrowing Casting (manually) - converting a larger type to a. byte -> short -> char -> int -> long -> float -> double. In Java, there are two types of casting: Widening Casting (automatically) - converting a smaller type to a larger type size. Abstract ClassĪ class which contains the abstract keyword in its declaration is known as abstract class.Ībstract classes may or may not contain abstract methods, i.e., methods without body ( public void get() )īut, if a class has at least one abstract method, then the class must be declared abstract. Type casting is when you assign a value of one primitive data type to another type. In Java, abstraction is achieved using Abstract classes and interfaces. A method may be implemented in several classes along the inheritance chain. In other words, the user will have the information on what the object does instead of how it does it. Polymorphism means that a variable of a supertype can refer to a subtype object. Likewise in Object-oriented programming, abstraction is a process of hiding the implementation details from the user, only the functionality will be provided to the user. Therefore, to send an e-mail you just need to type the content, mention the address of the receiver, and click send. In other words, polymorphism allows you define one. For example, when you consider the case of e-mail, complex details such as what happens as soon as you send an e-mail, the protocol your e-mail server uses are hidden from the user. Polymorphism is the capability of a method to do different things based on the object that it is acting upon. As per dictionary, abstraction is the quality of dealing with ideas rather than events.
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