Book Image

Java Fundamentals

By : Gazihan Alankus, Rogério Theodoro de Brito, Basheer Ahamed Fazal, Vinicius Isola, Miles Obare
Book Image

Java Fundamentals

By: Gazihan Alankus, Rogério Theodoro de Brito, Basheer Ahamed Fazal, Vinicius Isola, Miles Obare

Overview of this book

Since its inception, Java has stormed the programming world. Its features and functionalities provide developers with the tools needed to write robust cross-platform applications. Java Fundamentals introduces you to these tools and functionalities that will enable you to create Java programs. The book begins with an introduction to the language, its philosophy, and evolution over time, until the latest release. You'll learn how the javac/java tools work and what Java packages are - the way a Java program is usually organized. Once you are comfortable with this, you'll be introduced to advanced concepts of the language, such as control flow keywords. You'll explore object-oriented programming and the part it plays in making Java what it is. In the concluding chapters, you'll get to grips with classes, typecasting, and interfaces, and understand the use of data structures, arrays, strings, handling exceptions, and creating generics. By the end of this book, you will have learned to write programs, automate tasks, and follow advanced courses on algorithms and data structures or explore more advanced Java courses.
Table of Contents (12 chapters)
Java Fundamentals

Abstract Classes and Methods

Earlier, we discussed interfaces and how they can be useful when we wish to have a contract with our classes on the methods they have to implement. We then saw how we can only cast classes that share the same hierarchy tree.

Java also allows us to have classes with abstract methods that all classes inheriting from it must implement. Such a class is referred to as an abstract class and is denoted by using the abstract keyword after the access modifier.

When we declare a class as abstract, any class inheriting from it must implement the abstract methods in it. We cannot instantiate abstract classes:

public abstract class AbstractPerson {
     //this class is abstract and cannot be instantiated

Because abstract classes are still classes in the first place, they can have a logic and state of their own. This gives them more advantages compared to interfaces whose methods are empty. In addition, once we inherit from an abstract class, we can perform typecasting along...