Java is one of the most popular programming languages in the world, used to build applications ranging from simple widgets to complex enterprise software. It is the foundation of Android, along with its many other applications, and it is both powerful and versatile. Understanding the basics of Java classes is essential for its mastery – learning about the different types of Java classes, their definitions, object oriented programming, access modifiers, properties, constructors and more. In this article, we will explain Java classes in depth.

What are the Different Types of Java Classes?

The three main types of Java classes are concrete class, abstract class and interface. Concrete classes are classes that can be instantiated, and their methods can be implemented. Abstract classes are classes that cannot be instantiated, but they contain methods that may be implemented by any implementing class. An interface is an abstract class that provides a contract between implementations and contains certain methods that must be implemented by each implementation.

Concrete classes are the most commonly used type of Java class. They are used to define objects and their behavior. Abstract classes are used to define the structure of a class, but they cannot be instantiated. Interfaces are used to define a contract between different classes, and they are used to ensure that all implementations of a certain interface adhere to the same set of rules.

Java Class Definition

A class in Java is a blueprint of an object, consisting of variables and methods that define the structure and behavior of the object. In Java, a class is defined with the class keyword, followed by the name of the class. Inside a class, variables and methods can be defined.

Variables are used to store data, and methods are used to perform operations on the data. Variables and methods can be declared as public, private, or protected, which determines the scope of the variable or method. Public variables and methods can be accessed from anywhere, while private variables and methods can only be accessed within the class. Protected variables and methods can be accessed within the class and any subclasses.

Object Oriented Programming in Java

Java is an object-oriented programming language, which means that it focuses on programming using objects rather than using procedures and functions. Objects are instances of classes with their own set of variables and methods. An object can send messages to other objects and receive information from them. Object-oriented programming promotes reuse and organization of code, making it more efficient.

Object-oriented programming also allows for the creation of complex data structures, such as linked lists and trees. This makes it easier to store and manipulate data in a structured way. Additionally, object-oriented programming allows for the creation of abstract data types, which can be used to represent real-world objects. This makes it easier to model real-world problems in code.

Access Modifiers and Their Impact on Classes

In Java, access modifiers control the visibility of data within a class. The four access modifiers are public, protected, private and default. Public access modifiers are the most visible and can be accessed from outside the class. Protected access modifiers can be accessed from within the same package or any derived class. Private access modifiers can be accessed only from within the same class. Default access modifiers can be accessed only from within the same package.

It is important to understand the implications of each access modifier when designing a class. For example, if a class is designed to be used by other classes, then public access modifiers should be used. On the other hand, if a class is designed to be used only within the same package, then default access modifiers should be used. By understanding the implications of each access modifier, developers can ensure that their classes are designed in the most secure and efficient manner.

Properties of a Class In Java

A class has several properties that define its characteristics. These are the name of the class, its visibility (public, private, protected or default), its superclass (if any) and any interfaces that the class implements. In addition to these properties, a class may contain constructors, methods, fields, nested classes and interfaces.

Constructors in Java Classes

Constructors are special methods that are used to create an instance of a given class. The constructor is called when an instance of a class is created and it performs any necessary operations before the object is used in the program. Constructors usually take different values as arguments so that they can be used to create different instances with different initial states.

Interfaces and Abstract Classes in Java

Interfaces and abstract classes are two different types of Java classes that can be used for code reuse and code organization. An interface is an abstract class that provides a contract between implementations, meaning that its methods must be implemented by each implementation. An abstract class is a class that cannot be instantiated but it contains methods that may be implemented by any implementing class.

Extending Classes in Java

In Java, a class can extend another class through inheritance. When a class extends another class, it inherits all its members – variables, methods and constructors – as though they were declared within its own class body. Through inheritance, classes become more powerful and concise; however, they can still have their own fields and methods that do not exist in the superclass.

Wrapper Classes and Their Functionality

Java offers wrapper classes for all primitive data types such as int, double and char. A wrapper class is a class that wraps its data type so that it can be used conveniently in objects. Wrapper classes provide useful features such as conversion between various data types, string representations of values and arithmetic operations on values.

Comparing Primitive and Reference Types

Primitive types are basic data types such as int, double and char. They are stored directly in the memory and do not require any special operations or data structure to access their values. Reference types are complex data types such as objects and arrays that are constructed from primitive types. They are stored indirectly in the memory using references or pointers.

Commonly Used Java Classes

Some of the most commonly used Java classes are String, Math, Random, ArrayList, LinkedList, HashMap and Date. The String class provides various methods for manipulating strings such as concatenation, substrings and formatting. The Math class provides various mathematical operations such as trigonometric functions, logarithmic functions and rounding values. The Random class allows the generation of random numbers while others like ArrayList and HashMap are widely used for data storage.

Tips for Making the Most of Your Java Classes

When writing classes in Java, there are several tips to keep in mind to make the most out of them. Firstly, use inheritance judiciously since it can lead to complicated code paths. Secondly, make use of common libraries to take advantage of existing implementations rather than creating your own. Last but not least, use interfaces for code organization since they provide contracts between implementations.

Conclusion

Understanding Java classes is essential for mastering the language. In this article we have examined the different types of Java classes, their definitions, object oriented programming, access modifiers, properties, constructors and more. We have also discussed interfaces and abstract classes, extending classes in Java, wrapper classes and finally tips for taking full advantage of all the features available in Java classes.