abstract class extends abstract class java

What is an abstract class?
An abstract class is a class that is declared abstract —it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed. An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon), like this:
Should you use abstract classes in Java 8?
Note that code reuse is a very compelling reason to use abstract classes, as long as the “is-a” relationship within the class hierarchy is preserved. And Java 8 adds another wrinkle with default methods, which can sometimes take the place of needing to create an abstract class altogether. 4. A Sample Hierarchy of File Readers
Can abstract class extend concrete class?
I earlier learned that abstract class can extend concrete class. Though I don't see the reason for it from Java designers, but it is OK. I also learned that abstract class that extends concrete class can make overridden methods abstract. Why? Is there a use case where it is useful?
Can an interface extend an abstract class?
Whenever you extend an abstract class you should make sure that ALL the methods in the abstract class must be implemented in the sub class, or else it will lead to compilation error.. Key points to keep in mind before working with interfaces/abstract classes => Interfaces by definition cannot extend a class.

Overview

There are many cases when implementing a contract where we want to postpone some parts of the implementation to be completed later. We can easily accomplish this in Java through abstract classes. In this tutorial, we’ll learn the basics of abstract classes in Java, and in what cases they can be helpful. baeldung.com

Key Concepts For Abstract Classes

Before diving into when to use an abstract class, let’s look at their most relevant characteristics: 1. We define an abstract class with the abstract modifier preceding the classkeyword 2. An abstract class can be subclassed, but it can’t be instantiated 3. If a class defines one or more abstract methods, then the class itself must be declared abst

When to Use Abstract Classes

Now, let’s analyze a few typical scenarios where we should prefer abstract classes over interfacesand concrete classes: 1. We want to encapsulate some common functionality in one place (code reuse) that multiple, related subclasses will share 2. We need to partially define an API that our subclasses can easily extend and refine 3. The subclasses ne

A Sample Hierarchy of File Readers

To understand more clearly the functionality that abstract classes bring to the table, let’s look at another example. baeldung.com

Conclusion

In this quick article, we learned the basics of abstract classes in Java, and when to use them for achieving abstraction and encapsulating common implementation in one single place. As usual, all the code samples shown in this tutorial are available over on GitHub. baeldung.com

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