Java tutorial for beginners

Java is one of the world’s most powerful and widely used programming languages. Whether you’re a complete beginner or someone switching from another language, this Java guide will help you get started with the fundamentals and gradually build your expertise. Java is known for its platform independence, object-oriented nature, and wide applicability, making it a go-to language for software development, web applications, and enterprise solutions.

What will we cover in the Java tutorial?

This Java tutorial follows a structured, hands-on approach:

1. Start with the basics: Understand variables, data types, and operators with easy-to-follow examples.

2. Control your code: Learn conditional statements and loops to make your programs smart and dynamic.

3. Work with data: Explore arrays and dictionaries to handle real-world information.

4. Make it interactive: Master user input and functions to create programs that respond to real users.

5. Hands-on practice: Solve problems, complete exercises, and build small projects to reinforce what you learn!

By the end of this tutorial, you will have a strong understanding of Java syntax, key concepts, and practical implementations, which will help you begin your programming journey.

All about Java#

Java is a high-level, object-oriented language that Sun Microsystems (now Oracle) introduced in 1995. Its hallmark is the Java virtual machine (JVM), which lets you “write once, run everywhere” by interpreting bytecode on any supported platform, avoiding separate compilations for Windows, macOS, Linux, and more.

Java boasts extensive libraries and tools, both free and open-source, for everything from simple mobile apps to large-scale enterprise systems.

What makes Java so popular?#

Whether working on a personal project or building powerful business systems, Java provides a dependable platform for software development.

Setting up the Java environment#

To start coding in Java, you’ll first need to install the Java Development Kit (JDK), which comes bundled with both the compiler (javac) and the runtime (java). Here’s how to set it up across different operating systems.

1. Install the Java Development Kit (JDK)#

You can download and install the latest JDK from Oracle’s official website or use OpenJDK, an open-source alternative widely used in production environments.

Both versions work across Windows, macOS, and Linux.

2. Set up environment variables#

For Windows users#

• Open System Properties → Advanced system settings → Environment Variables.

• Under “System Variables,” find Path, click Edit, and add the JDK bin directory, typically: C:\Program Files\Java\jdk-XX\bin

For macOS users#

• If you installed via Homebrew, Java should automatically be linked. You can check by running:

• Optionally, add the following to your shell profile (.bash_profile, .zshrc, etc.):

For Linux users#

• If you installed via package manager (apt, yum, etc.), environment variables are usually set automatically.

• To set manually, add this to your .bashrc or .zshrc.

3. Verify the installation#

Once you’ve completed the setup, verify everything is working by running:

If the installation is successful, you’ll see the installed Java version displayed in your terminal or command prompt.

4. Install an IDE (integrated development environment)#

Using an IDE simplifies coding with features like syntax highlighting, debugging, and auto-completion. Popular IDEs include:

• IntelliJ IDEA (preferred for Java development)

• Eclipse

• NetBeans

• VS Code (with Java extensions)

Write your first Java program#

Let’s write a simple Java program to print ‘Hello, World!’. To use any method in Java, we must make a call to it. This can be done by writing the method’s name, followed by a set of opening ( and closing ) parentheses. Inside the parentheses, we can provide the inputs to the method, like in line 3 below.

Here,

• public class HelloWorld: This defines a class named “HelloWorld.”

• public static void main(String[] args): This is the main method where program execution begins.

• System.out.println(): This prints text to the console, which in our case is “HelloWorld,” and then moves the cursor to a new line for future output. We have another option, System.out.print(), that prints the text but keeps the cursor on the same line so that any following output will appear right next to it.

Java syntax and basic concepts#

Java is a powerful, object-oriented programming language. Its syntax forms the foundation of how you write and execute code. Understanding the basic building blocks, including variables, data types, and operators, is important for building efficient and effective programs.

Variables and data types#

In Java, variables store data that can be referenced and manipulated throughout your program. Since Java is a statically typed language, each variable must be declared with a specific data type, which defines what kind of value the variable can hold (such as numbers, characters, or text).

Operators in Java#

Operators are special symbols used to perform operations on variables or values. Java provides a variety of operators, including arithmetic, relational, logical, bitwise, and assignment operators. These operators allow you to perform calculations, comparisons, and logical operations.

Here,

• a + b uses the arithmetic operator + to add a and b, outputting 15.

• a > b uses the relational operator > to compare a and b, and since 10 is greater than 5, it returns true.

• a > 5 && b < 10 uses the logical operator && to combine two conditions. Both conditions (a > 5 and b < 10) are true, so the result is true.

Methods#

In Java, a method is a reusable block of code designed to perform a specific task. Methods help in breaking down a complex program into smaller, manageable pieces. They improve readability, simplify debugging, and enable code reusability. Methods typically accept inputs (called parameters) and may return a result.

Here’s an example demonstrating method definition, calling, and returning values:

Note: Vertically scroll down in the code widget below to see the complete code.

In this example, we define two methods: add and greet. The add method accepts two integer parameters, calculates their sum, and returns the result. The greet method accepts a String parameter (name) and prints a greeting message. Within the main method, we call add(10, 20), storing the result in the variable result, and then print it. We also call greet("Alice") to display a personalized greeting.

Input and output#

In Java, input refers to data or information received from users or external sources, typically through the keyboard, files, or other devices. The most common and straightforward way to handle user input is through the Scanner class.

On the other hand, output means displaying data or information back to users, commonly via the console. Java provides built-in methods like print(), println(), and printf() for displaying output clearly and conveniently.

Combining these two concepts allows your programs to interact dynamically with users, taking information from them, processing it, and presenting the results.

Note: Before running the code, enter your name and age in the input section below the widget, each on a separate line, as follows:

• Name

• Age

Control flow (conditional statements)#

Control flow statements allow you to direct the execution of your program based on certain conditions. Using these statements, you can make decisions, execute specific code blocks, and ensure your program behaves dynamically based on different inputs or situations. In Java, two common types of control flow statements are the if-else statement and the switch-case statement.

If-else statement#

The if-else statement is one of the most fundamental control flow mechanisms in programming.

It allows you to test a condition (a boolean expression) and decide which block of code to execute based on whether it is true or false.

In this example:

• The program checks if the value of age is greater than or equal to 18.

• If the age is 18 or older, the program prints “You are an adult.”

• If the age is less than 18, the program prints “You are a minor.”

Switch case#

The switch statement offers an alternative way to handle multiple conditions. Unlike the if-else chain, the switch case compares a single variable against multiple constant values.

It’s more concise and often easier to read when there are many possible conditions to evaluate.

In this example:

• The switch statement evaluates the variable day and checks which case matches the value.

• If day equals 1, it prints “Monday.”

• If day equals 2, it prints “Tuesday.”

• If none of the cases match (e.g., if day is not 1 or 2), it executes the default case and prints “Other day.”

Challenge: Wizard’s weekly routine#

Loops in Java#

Loops are a fundamental concept in programming. They enable you to repeat a block of code multiple times. Loops are especially useful when you need to perform repetitive tasks without manually writing the same code repeatedly.

The for Loop#

The for loop is one of the most commonly used loops in Java. It is used when you know how often you want to execute a statement or a block of statements.

A for loop consists of initialization, condition, and iteration.

• Initialization: int i = 0 sets the loop variable i to 0.

• Condition: i < 5 checks if i is less than 5. The loop will run as long as this condition is true.

• Iteration: i++ increments i by 1 after each iteration.

• The loop will print "Iteration: 0", "Iteration: 1", and so on, up to "Iteration: 4", because when i becomes 5, the condition i < 5 is no longer true, and the loop exits.

The while loop#

The while loop is used when you want to repeat a block of code indefinitely as long as a specified condition is true.

The key difference from the for loop is that the condition is evaluated before each iteration, and there is no explicit iteration in the loop syntax itself.

• Initialization: int i = 1 sets i to 1.

• Condition: i <= 5 checks if i is less than or equal to 5. The loop runs as long as this condition is true.

• Iteration: i++ increments i by 1 after each iteration.

• The loop will print "Iteration 1", "Iteration 2", and so on, up to "Iteration 5". When i becomes 6, the condition i <= 5 becomes false, and the loop exits.

Arrays#

An array in Java is a data structure that allows you to store a fixed-size sequence of elements of the same data type. It’s particularly useful when storing multiple values of similar data together—for instance, a list of numbers, names, or scores.

Arrays provide convenient access to data using index positions, starting at index 0 for the first element. Let’s understand this with the help of an example:

Here’s an example demonstrating how to declare, initialize, and access elements in an array:

In the example above, we first declare and initialize an integer array named numbers with five values (10, 20, 30, 40, 50). We access individual elements using index positions (numbers[0] for the first element and numbers[2] for the third). Finally, we iterate through the array using a for loop, where the loop counter i starts from 0 and continues until it reaches the array’s length (numbers.length), printing each array element sequentially.

Multidimensional arrays#

A multidimensional array in Java is an array of arrays, often used to represent data in a tabular format (rows and columns). A common example is a two-dimensional (2D) array, which can store data as a table, grid, or matrix. Each element is accessed using two indexes: one for the row and another for the column.

Let’s understand it with the help of an example  that shows how to declare, initialize, and access elements in a 2D array:

In this example, we declare and initialize a two-dimensional array named matrix, structured as three rows and three columns. We access specific elements using two indexes, [row][column], such as matrix[0][1] for the element in the first row and second column. To print all elements, we use nested for loops: the outer loop iterates over each row, and the inner loop iterates over each element within that row, printing the elements in a grid format.

Dictionary (map)#

In Java, a dictionary-like data structure called a map stores data as key-value pairs. Each key in a map is unique and corresponds directly to a specific value. Maps are widely used for fast retrieval, insertion, and deletion of data based on keys.

Java provides several implementations of maps, but HashMap is the most common. Here’s an example demonstrating how to create, populate, and access a Java dictionary (Map):

In this example, we created a HashMap called studentGrades to store student names (keys) and their corresponding grades (values). Using the .put() method, we added key-value pairs. We used the .get(key) method to access a specific student's grade. We then iterated through all the entries using the .keySet() method, displaying each student’s name and grade. Maps provide an efficient and convenient way to manage associated data in Java applications.

Challenge: Dragon’s Hoard Registry#

Expected output

OOP in Java#

Java is fundamentally an object-oriented programming language, which means it revolves around the concept of objects—instances of classes that bundle data and behavior together. This design makes Java programs modular, scalable, reusable, and easier to maintain, especially for large and complex systems.

OOP helps developers model real-world entities, define their attributes (fields) and behaviors (methods), and interact with them through well-structured code.

Classes and objects#

A class is like a blueprint or a template for creating objects. It defines objects’ properties (data) and methods (behavior). Think of a class as a detailed plan or design specification, whereas an object is an instance of a class.

Let’s take a real-world example: a library.

Create the library class

Creating book objects (Instances)#

Objects are created from the class, each representing individual books with their titles and statuses:

In this example, we defined a Library class with attributes bookTitle and isBorrowed, representing each book’s title and availability status. The class contains methods: setBookDetails() to set each book’s initial details, borrowBook() to handle borrowing logic by checking and updating the book’s availability, and displayBook() to show the current details. In the main method, two book objects (book1 and book2) are created and assigned unique details. We then attempt to borrow both books, demonstrating how each object’s state is managed independently, and finally, display the current details to showcase their updated status.

Java’s OOP principles are built on four key concepts.

Encapsulation (data hiding and control)#

Encapsulation hides an object’s internal state and requires all data interaction to happen through methods. This prevents external code from directly accessing sensitive information and enforces control over how the data is modified or retrieved.

Let’s understand it with the help of a bank account example.

Inheritance (reusability and hierarchical design)#

Inheritance allows a new class (child/subclass) to acquire properties and methods from an existing class (parent/superclass).

This promotes code reuse, reduces duplication, and reflects real-world hierarchical relationships. Let’s understand it with the help of an example.

Here, the Dog class inherits the eat() method from Animal and adds its own bark().

Polymorphism (one interface, multiple forms)#

Polymorphism means ‘many forms.’  In Java, this allows methods to behave differently in Java based on the object calling them.

There are two main types:

• Compile-time polymorphism (method overloading)

• Runtime polymorphism (method overriding)

Let’s understand the most commonly used method of overriding with the Animal and Cat example:

Here, calling sound() on a Cat object prints “Meow”, even though sound() is defined in the Animal class.

Abstraction (hiding complexity, showing functionality)#

Abstraction means hiding the complex internal logic and exposing only essential features to the user. It allows you to work with “what” an object does, not “how” it does it.

Here’s an example of an abstract Animal class:

In this example, we defined an abstract class Animal that contains an abstract method makeSound() (without any implementation) and a concrete method eat() (with implementation). The subclass Dog extends the Animal class and provides the specific implementation for the abstract method makeSound(). In the main method, we create an object of the subclass Dog and invoke both methods. This demonstrates how abstraction allows us to define a general behavior (makeSound()) that each subclass must specifically implement, while also providing shared behaviors (eat()) across subclasses.

Conclusion#

Learning Java opens up many opportunities, from building web applications to developing mobile apps. This guide introduced you to Java’s syntax, object-oriented programming, collections, exceptions, and file handling. The key to becoming proficient is practice—try writing programs, experimenting with concepts, and building small projects. As you progress, explore advanced topics like multithreading, JDBC, and frameworks like Spring and Hibernate. Keep coding, and enjoy your journey with Java!