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Computer Network. Compiler Design. Computer Organization. Discrete Mathematics. Ethical Hacking. Computer Graphics. All GraphicObject s must be able to draw or resize themselves; they just differ in how they do it.
This is a perfect situation for an abstract superclass. You can take advantage of the similarities and declare all the graphic objects to inherit from the same abstract parent object for example, GraphicObject as shown in the following figure. First, you declare an abstract class, GraphicObject , to provide member variables and methods that are wholly shared by all subclasses, such as the current position and the moveTo method.
GraphicObject also declares abstract methods for methods, such as draw or resize , that need to be implemented by all subclasses but must be implemented in different ways. The GraphicObject class can look something like this:. Each nonabstract subclass of GraphicObject , such as Circle and Rectangle , must provide implementations for the draw and resize methods:.
In the section on Interfaces , it was noted that a class that implements an interface must implement all of the interface's methods. It is possible, however, to define a class that does not implement all of the interface's methods, provided that the class is declared to be abstract.
For example,. In this case, class X must be abstract because it does not fully implement Y , but class XX does, in fact, implement Y. An abstract class may have static fields and static methods. Here, the subclass Dog provides the implementation for the abstract method makeSound. We then used the object d1 of the Dog class to call methods makeSound and eat. Note : If the Dog class doesn't provide the implementation of the abstract method makeSound , Dog should also be declared as abstract.
This is because the subclass Dog inherits makeSound from Animal. An abstract class can have constructors like the regular class. And, we can access the constructor of an abstract class from the subclass using the super keyword.
Here, we have used the super inside the constructor of Dog to access the constructor of the Animal. Note that the super should always be the first statement of the subclass constructor. Visit Java super keyword to learn more. Abstraction is an important concept of object-oriented programming that allows us to hide unnecessary details and only show the needed information.
This allows us to manage complexity by omitting or hiding details with a simpler, higher-level idea. A practical example of abstraction can be motorbike brakes. We know what brake does. When we apply the brake, the motorbike will stop. However, the working of the brake is kept hidden from us. The major advantage of hiding the working of the brake is that now the manufacturer can implement brake differently for different motorbikes, however, what brake does will be the same.
In the above example, we have created an abstract super class MotorBike. The superclass MotorBike has an abstract method brake. The brake method cannot be implemented inside MotorBike.
It is because every bike has different implementation of brakes. So, all the subclasses of MotorBike would have different implementation of brake. Here, MountainBike makes its own implementation of brake and SportsBike makes its own implementation of brake. Note : We can also use interfaces to achieve abstraction in Java. To learn more, visit Java Interface. Course Index Explore Programiz.
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