Learn Data Abstraction in Java

Whenever the term data abstraction is used, it means that the data is hidden to some extent. It is only through this property that important information is made available to the user. All data which are not necessary are made abstract or hidden from the data. If an object is considered, then data abstraction means that essential characteristics of the objects are identified while all sorts of irrelevant data are ignored. Whenever a group of objects is considered, their properties and features make the object different from the other objects belonging to the same class. 

The concept of data abstraction can be explained through a real-life example. Let us consider an example where a driver riding a vehicle knows that applying brakes will stop the vehicle from moving further. So the only information the driver knows is that he has to stop his vehicle from moving, so he applies the brakes. But he doesn’t know the underlying mechanism as to how the vehicle stops when a brake is applied. So this concept can be compared to the data abstraction concept where only the information required to be known to the user is displayed. The underlying information is kept hidden. So, this is the concept of abstraction, and when it is applied in the data, it is known as data abstraction.

Object-Oriented Programming provides ways for utilizing the data abstraction concept. Java is one of Object-Oriented Programming, follows the feature of data abstraction. In these programming languages, abstract classes and interfaces are used for achieving data abstraction.

The process of data abstraction in Java is achieved through the class’s abstract classes. Interfaces are also used for data abstraction apart from abstract classes. The keyword “abstract” is used as a non-access modifier for the methods and classes. When defined with the keyword access, a class is an abstract class where the creation of objects is not allowed. Accession of the abstract class is only possible if it is inherited from another class. Abstract methods are those methods that can be used only in abstract classes. These methods don’t have a method body. 

The subclass generally provides the body. Abstract classes can contain methods that are both regular and abstract.

Differences between an abstract class and an abstract method 

The differences between an abstract class and an abstract method are:

1. The abstract classes are those classes that are declared with the keyword abstract.

2. An abstract method is such a type of method which gets declared without its implementation.

3. An abstract class doesn’t need to have all the abstract method methods within itself. It can also contain methods that are not abstract.

4. Whenever a method is defined as an abstract method, it should also be defined again in the subclass. This will make the overriding compulsory and also make the subclass abstract.

5. If any class contains any abstract methods, whether one abstract method or more than that, it should be declared abstract by using the keyword abstract.

6. An abstract class cannot contain any object. A new operator cannot be used to instantiate the abstract class.

7. There is always the presence of default constructors in an abstract class. Also, parameterized constructors can be present in an abstract class.

Java Abstract class

The programming language Java implements abstraction through abstract classes. An abstract class may be defined as that class that is declared with the keyword “abstract” with a special instruction that these classes cannot get instantiated. These classes may contain or may not contain abstract methods. 

The syntax of an abstract class in Java is shown below.

The above code is taken from https://www.softwaretestinghelp.com/what-is-abstraction-in-java/.

In the above syntax, it can be observed that both the abstract and the non-abstract methods can be contained within an abstract class. Also, the keyword “abstract” is placed before the declaration of the class. 

Read more about the java abstract class here 

Java Abstract Method

Java abstract methods are those methods that are preceded by the keyword “abstract,” but there is no implementation of the methods. The Java abstract methods are declared within the Java abstract class.

Because of the abstract methods, the Java abstract class becomes incomplete because the methods cannot be implemented. Therefore, the inclusion of an abstract form in the abstract class naturally makes the abstract class incomplete.

Its implementation in the subclass can use the abstract method. This subclass will inherit the abstract class and will carry out the implementation of the abstract methods. The general syntax of the abstract method is 

abstract void methodName (parameter_list);

Few rules should be noted while writing the method of abstract

  • If a class contains more than one abstract method, then the class will become an abstract class.
  • There should not be any keywords other than “abstract” while defining the abstract class and methods.

Considering the above points, the following possibilities are not allowed in Java.

  • final
  • abstract native
  • abstract static
  • abstract private
  • abstract synchronized
  • abstract strictfp 

An example of data abstraction in Java is shown below.

https://www.javatpoint.com/how-to-achieve-abstraction-in-java.

The above code is taken from https://www.softwaretestinghelp.com/what-is-abstraction-in-java/.

In the code shown above, there is a class Bank. There is an abstract method within the Bank class which is getInterestRate(). Two other classes BOI and ICICI, are declared, which inherit the class Bank. These declared classes inherit the Bank class and therefore implement the method getInterestRate() returning the interest rates. 

An object of the Bank is created in the primary method. The object of the Bank consists of an ICICI class object which displays the interest rate. In the next step, the object of the class BOI is created too, which displays the interest rate. 

Data abstraction through the interface

Interfaces are similar to the Java classes, with the only difference being that there are empty methods in an interface. It can also be defined as classes that consist of abstract methods and static constants. Every method present in the interface is public, and it does not contain any constructor. The interface is used for achieving data abstraction, and also it is used for performing multiple inheritances in Java. 

A few features of interfaces in Java are:

  • The interfaces can be used for achieving total abstraction.
  • A single class can use multiple interfaces that lead to the achievement of multiple interfaces.
  • Interfaces allow achieving loose coupling.

The syntax of the interface is shown below:

The above syntax is used from https://www.javatpoint.com/how-to-achieve-abstraction-in-java.

An interface can be used through the keyword “implements.”

A few differences between the abstract classes and the interface are:

  • Both the abstract and also the non-abstract methods can be contained within the abstract classes. While, in an interface, only the abstract methods can be present.
  • Final variables may or may not be present in the abstract classes. In interfaces, the variables can be final as default variables.
  • The class abstract can have variables that are non-final, final, non-static, or static. While, in an interface, only static and final variables may be present.
  • The abstract class allows the implementation of interfaces. An abstract class cannot be implemented in an interface.
  • The inheritance of an abstract class is done through the keyword “extends.” Implementation of the interface is done through the keyword “implements.”
  • The abstract class can implement multiple interfaces, or other classes can be extended by the abstract class. Whereas an interface can allow implementation of only another interface.
  • Apart from public members, both data members that are protected and private are contained in an abstract class. Whereas the members of an interface are by default public. 

Read more differences between the abstract classes and interface here.

Conclusion

The article has described the concepts of data abstraction and has listed how data abstraction can be achieved in Java. For getting more experience in the Java programming language, you can check the Software Development Course offered by upGrad. The course is designed for working professionals and will train you with industry-oriented projects that will develop the required programming skills. More information can be retrieved through our website. For any information and help, our team of assistance can be contacted.

What do you mean by data abstraction in Java? Define data abstraction?

The concept of data subtraction hides any complex data and presents or shows only the functional data to the user.

How can data abstraction be achieved in Java?

In Java, data abstraction can be achieved in two ways:

1. Through using the abstract classes.
2. Through using the interface.

What does abstract class in Java mean?

Any class in Java which is declared with the keyword 'abstract' becomes an abstract class.

Abstract classes cannot be instantiated, but why are constructors allowed in an abstract class?

There cannot be objects created for an abstract class, but objects can be created for the sub-classes. From the constructor of the sub-class, there will be a call to the constructor of the super-class implicitly. Therefore, constructors must be present in an abstract class. Even if a user does not define any constructor in an abstract class, the compiler will by default generate a constructor.

What do you mean by an interface in Java?

An interface in Java has constants that are static and, by default ,consist of abstract methods.

When are the abstract methods used?

The abstract method is usually declared in the parent class when the user wants a class containing a specific method. Still also it wants the implementation of the method to be done by its subclass.

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