Whether you are a beginner or an experienced Java programmer, there are several core Java concepts that you should know. Learning programming languages like Java can be a challenge. Like other computer programming languages, Java has a lot of ins and outs that can seem overwhelming. 

How can you motivate yourself to learn? Well, keeping a positive perspective is key. For example, learning programming skills along with languages can change your life for the better. When you have strong programming skills, it becomes easier for you to expand your knowledge to more new languages and technologies.

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Fully understanding how Java programming works offers many benefits. For example, it will make your life easier when you are coding in Java. It will also help ensure that you spend less time debugging your programming. In many cases, you can use what you know as a key advantage in an interview.

This article can help reinforce your understanding of Java programming. You can use this article as a quick reference guide to tools and information on the important core Java concepts. To help you focus on Java core concepts, this article does not include any programming code. This is because we recommend that you understand these concepts before you begin coding in Java.

Whether you aim to be a Java Developer, Java Designer, or other Java role, Java classes can be useful tools. You may have already learned Java and need a refresher. This could be your first attempt at learning how to program. Alternatively, you may be an experienced programmer who is new to the Java programming language. In any of these scenarios, this article will be of interest to you. 

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Whether you are learning or reviewing the concepts that we discuss, you will ultimately rely on them when you code in Java. This article highlights some high-level Java core concepts and takes a deeper dive into other subtopics. Read on to learn about a number of Java concepts, including:

1. Interfaces

In Java, you will program to an interface instead of an implementation. This is also known as programming to interfaces, which refers to a way to write classes based on an interface that defines the object’s behavior. This design concept may seem like more work initially because you have to start with these three steps:

However, this Java workflow ensures that you are:

What’s great about these steps is that they make code more flexible and easier to test in Java.

2. Executing in Java

In Java, two basic units of execution are process and thread. Process and thread are defined in Java as follows:

Using threads in Java offers some valuable benefits:

Depending on your use case, Java also offers multithreading functionality. 

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3. Object-Oriented Programming (OOP)

An important concept in Java is OOP, which stands for object-oriented programming. Java is an OOP language, which means that it emphasizes data more than it does functions. OOP programming languages revolve around objects. 

This object bundles up data and the methods that operate on this data in one unit. This protects data by having the methods inside the object. In OOP, the objects communicate with each other through messages. All OOP languages (including Java) support the following features:

Polymorphism is an important feature of OOP. Polymorphism enables Java to allow objects or entities to assume multiple forms. A method with multiple implementations, for example, is polymorphic in Java. There are two types of polymorphism in Java:

4. Variables

In Java, variables are containers for storing data values. Java supports the following three types of variables:

You need to specify a data type for every variable. You should specify the data type when you declare the variable. Every variable should also have a unique (or non-duplicate) name to identify it. Java requires that you apply the following rules for naming variables:

It is also important to note that Java reserves certain words for its own use. These are known as Java keywords. Therefore, you can not use keywords as variable or identifier names. w3Schools contains a full list of Java keywords.

Java uses the following different data types of variables:

Once you declare a variable, you can:

5. Data Types

Java is a strongly typed language, which means every data or information has a set Data Type. Any variable that holds the value needs to hold a numeric or string or character. We call this the data type of the variable. Java uses Data Types to store different kinds of information. After you declare your Data Type in Java, you cannot change it. 

You can classify data Types into two categories: primitive data type and non-primitive data type.

6. Primitive Data Types

Primitive data types are not objects or references to objects. Java includes the following primitive data types:

Primitive number types can divide into two groups:

7. Non-primitive Data Types

Non-primitive data types are reference types because they refer to objects. The main difference between primitive and non-primitive data types are:

8. Operators

Operators are symbols that perform logical and mathematical operations on variables or identifiers. These operators help in performing operations. Java supports various operators, which include the following:

9. Classes and Objects

To put it simply:

In greater detail, classes are supported by every object-oriented programming language. In addition, you can use them to group related data. Data variables (also known as member variables) and methods depict the behavior of objects. These are known as instances of the class. In other words, an object defines the state of the entity represented by a class at any given instant. An object typically includes:

To understand the relationship between classes and objects in Java, you should consider the following:

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10. Packages

You can group classes and interfaces that have similar functionality or dependency to form a package. Packages give you more flexibility to group and organize your Java code.

11. Fields 

A field is a variable that belongs to a class or object. For instance, the Car Class could define a field called brand. All Car objects would have this brand field, but the value of this field can be different for each instance of the class. This allows Car objects to be different from one another while still sharing the basic attributes inherent to all cars.

12. Constructors

In Java, a constructor is a special method you can use to initialize objects. Java calls the constructor after you create an object of a class. You can also use constructors to set initial values for object attributes.

The purpose of constructors is to assign values to the fields that are specific to that particular instance of the object. For instance, if you are creating a Car object, you may need to tell the program what brand the car is, its color, how fast it is going, and in what direction it is traveling. A constructor allows you to do these things easily when the object is created during program execution.

13. Methods

Java supports the creation of methods. A method is a group of operations that carry out a certain function together. Methods take advantage of the OOP concept, encapsulation. Methods are useful for when you want to:

When you declare a method, it contains a method name, input parameters, and return type. This is known as a method signature. 

When you are learning about methods, note that it is very important to understand these two core Java concepts:

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Abstract Class and Methods

In Java, every class is a concrete class by default. To implement the abstract class, you need to use the abstract keyword before the class. This sets the class to an abstract class. 

Abstract classes in Java do not map to real-life objects. They cannot exist on their own unless they take the form of their respective concrete subclasses.

Using an abstract class in Java offers several advantages, which include:

It is important to note that while you can create a reference for an abstract class, you cannot create an object of an abstract class. An additional benefit of using abstract classes is that it gives you the ability to define abstract methods.

Abstract methods are methods that have only the declaration and do not have a definition. In Java, declaration and definition entail the following: 

As a friendly reminder, the method signature includes the method name, input parameters, and return type. 

Once you have a basic understanding of these principles, you can start creating your own Java programs. Many of these concepts may seem slightly abstract when they are new to you. After you start coding in Java, all the pieces will come together. Java programming offers many benefits that will lay the groundwork for your success as a Java programmer.

Page Last Updated: January 2022