What is a Class in Java? A Guide to Classes and Objects

Since its inception, the Java programming language has become one of the most popular languages, especially for enterprise applications. According to the PYPL Popularity of Programming Language Index, Java is the second most popular language right behind Python.

Java is an object-oriented programming (OOP) language. OOP languages share common elements, including classes, objects, polymorphism, inheritance, etc. What are these elements, and why do they matter?

Continue reading to learn more about Java and some of the key concepts associated with this OOP language. 

An Overview of the Java Programming Language

The creators of Java wanted the language to achieve five critical goals:

• Java should be safe and strong.
• Java should function well.
• Java should be easy to learn, distributed and object-oriented.
• Java should support parallelism, use dynamic typing and have an interpreter written for it for better portability.
• Java should not depend on any other platform or computer architecture.

While many introductory coding courses focus on teaching Java, it’s still widely used by professional programmers. For example, Java is often used in tandem with Scala, another programming language, particularly for artificial intelligence (AI) programming tasks.

The language is famous for its slogan, “write once, run anywhere” (WORA), and allows programmers to write Java code on one system and run it on any other Java-enabled system without making any changes.

What is a Class in Java?

Because Java is object-oriented, this means that it’s core elements are classes and objects. A class in Java is a set of instructions, or a template, used to create specific objects. Developers must also determine what the object should contain and how it behaves. 

Classes in Java are centered around real-world entities, and the objects in a Java class work together to make a program function properly. In general, Java class declarations include these components, in order:

• Modifiers
• Class keyword
• Class name
• Superclass
• Interfaces
• Body

Several types of classes are used for real-time applications, such as lambda expressions, nested classes and anonymous classes. In many programming instances, you will have to create many objects of the same type, depending on the project. 

Creating a Class in Java

In order to understand how to create classes, you must first become familiar with Java Syntax, or the basic language used to write programs, so the compiler and computer can understand it. Every line of Java code must be inside a class, and because Java is case-sensitive, every class must start with a capital letter.

Below is the syntax of a Java class:

class <class_name>{  

    field;  

    method;  

  }

Java classes consist of objects sharing similar properties and methods. Therefore, all objects in a given class will have the same methods or properties.

What is the Difference Between a Class and Object in Java?

Objects are different from but closely related to Java classes. An object is an instance of a class. It’s a self-contained component with methods and properties that make a specific type of data useful. 

In programming, objects can be data structures, a variable or a function. Java objects consist of the following:

• State
• Behavior
• Identity

A class, on the other hand, is simply a blueprint used to create individual objects. Think about Java objects as if they are the building blocks of a Java class. For example, the object “dog” would have these characteristics in Java, which correspond to what is found in the real world:

• State: Breed, age, color, weight, etc.
• Behavior: Bark, sleep, play, eat, drink
• Identity: Dog’s name

Within a Java class, all of the instances (a.k.a. objects) share the same attributes and behavior, but the value of those attributes (a.k.a state) is unique for each project. In other words, objects can share the same code but have different behaviors based on their values.

Creating an Object in Java

A single Java class can have any number of objects. You can create Java objects using one of the five methods, listed below with their syntaxes:

• Java new operator (most popular)
  • class_name object_name = new class_name()  
• Java Class.newInstance() 
  • public T newInstance() throws IllegalAcccessException, InstantiationException  
• Java newInstance() method of constructor
  • public T newInstance(Objects…initargs)  
• Java Object.clone() 
  • protected Object clone() throws CloneNotSupportedException 
• Java Object Serialization and Deserialization
  • Serialization: public final void writeObject(Object obj) throws IOException  
  • Deserialization: public final Object readObject() throws IOException  

Other Tips for Java Beginners

After acquiring Sun Microsystems in 2010, Oracle Corporation became the official owner of Java. Thankfully, Oracle published The Java Tutorials, a set of practical guides to help newcomers and experienced developers work on improving their knowledge of Java. 

Oracle also offers Java Tutorials Learning Paths to help newcomers and programmers trying to bolster their skills.

You can choose from four Java learning paths based on your experience level. The paths include:

• New to Java
• Building On The Foundation
• Cherish The Client?
• Fervor Over Server!

Additionally, you can access a slew of helpful information and resources on Oracle’s Java Documentation webpage, such as:

• Rich set of code samples
• Developer guides
• API documentation
• Tutorials
• And more

Oracle’s Java documentation site also provides brief overviews of Java Platform SE (standard edition), Java Embedded and Java Platform EE (enterprise edition). 

Understanding Java and Its Various Components

Anyone interested in programming should understand the value of learning Java. The programming language has a plethora of real-world applications and is used by a wide range of companies. Therefore, having a strong background and exceptional working knowledge of Java can help you earn an entry-level position and launch your career.