Abstraction in Java refers to hiding the program's implementation and showing only the functionality. It means the user will not be able to interact with the internal details of the code. 

In Java, it can be done with the help of either using an interface or an abstract class. However, the preferred method is to use abstract classes in Java. 

Moreover, it makes sense as the name of this class itself refers to the word abstraction. But, a commonly asked question about the abstract classes in Java makes it different from the regular classes. So let's find out.

We will also touch upon the concept of Java arrays. Let’s get started!

What is an abstract class in Java?

Abstract class in Java is the encapsulated blueprint of the program. It doesn't allow the user to access the components of programs and only lets the user explore the program's functionality. 

Moreover, the abstract class in Java can't instantiate itself. To better understand the abstract class in Java, you should know about its components. 

Abstract keyword

An abstract class always has abstract keywords, which declares the class as an abstract class in Java. The keyword used to declare an abstract class looks like "abstract." 

Abstract Method

Abstract methods are like regular methods with nobody. It means the body containing the code elements is not shown in the abstract method. Moreover, if a concrete class extends the abstract method, the "abstract" should be used to keep it abstracted. 

Regular Method

Regular methods in abstract class can also exist if there is a need to show the body that a method contains. 

Constructors

The instance variables in the abstract class are initiated with the help of constructors. Constructors are one of the most essential elements of an abstract class. 

What is the difference between the regular and abstract classes in Java?

Now, let's understand the differences between regular Java classes and abstract Java classes. Here are the points where these two types of classes can be differentiated. 

Purpose 

The first major difference is the purpose of these two classes. The regular classes are used to draft programs and algorithms in Java. On the other hand, the abstract class in Java helps ro hide the code structure and display the function of the code. 

Instantiation

The regular classes can be instantiated with the help of the "new" keyword. However, the abstract class in Java cannot instantiate by itself using the "new" keyword.

Object Creation

Regular Java classes create objects with unique data and behavior. On the other hand, abstract classes act as the blueprint of the object with no data and behavior visible to the user. 

Abstract Methods

In regular classes, you can not create abstract classes, as having a body for a method in a regular class is necessary. Moreover, if you try to create an abstract method in a regular class, it will neither work nor make sense. However, the abstract method is present in the abstract class with no body of the object in the respective regular class. 

Concrete subclasses

Concrete subclasses in regular classes can be instantiated directly. Moreover, you can also extend it to other classes. But in the abstract class, only extending works and not instantiation. 

Method Implementation 

Method Implementation in regular classes is done within the class. However, abstract classes in Java use abstract methods which can only be implemented by subclasses extension. 

What are the benefits of using abstract classes in Java?

Code Organization

Abstract class in Java allows you to organize the code. It also makes it easy to reuse the components of code in other projects. 

Consistent Interface

It provides a consistent interface with the same structure and behavior used in the whole program. 

Abstraction of Details

It is a great tool to introduce the program's interface to someone. Abstract class in Java showcases what a program does and not it does. 

Encapsulation

Abstract classes encapsulate related methods and properties in a single unit, reducing code duplication and adhering to the principles of encapsulation in object-oriented programming.

What is Interface in Java and How does it differ from Abstract class?

Java interface is another feature that works similarly to abstract classes in Java. Moreover, there are many similarities that you can find between interface and abstract class in Java. 

Firstly, abstract methods are used in the interface to hide the method body. It is also implemented with the help of keywords, as we do in abstract class. 

However, the keyword is the first difference between the interface and abstract class. In interface, the "interface" keyword is used. On the other hand, in the abstract class, "abstract" is used to achieve abstraction. 

Now, onto the second and the significant difference between abstract class in Java and interface. The abstract class doesn't facilitate using multiple Inheritance as it is not possible in Java itself. 

However, with the interface, you can use multiple Inheritance in the abstraction of a program. It is done with the help of a concept called hybrid Inheritance in Java. 

What is Array in Java?

An array in Java is like a row of boxes that can hold different pieces of information. The boxes have a fixed number, and each box can store a specific data type. For example, an array in Java with "int" can hold only integers.

One helpful thing about arrays in Java is that they have a proper indexing system. So, you can easily find and use the information stored in any box using its number. It's like having an address for each box in the row.

Conclusion

Abstract class in Java is best to achieve encapsulation and polymorphism.

Moreover, the primary purpose of abstract class in Java, which is an abstraction of a program, is also done in a very sophisticated manner. 

Using abstract classes is always preferred when it comes to abstraction in Java. It is also chosen over the interface, which is another way to achieve abstraction in Java. Interfaces in Java are only used if there is a need for multiple inheritance during abstraction.