How to Build Your First Java Application

Table of Contents

1. Fundamental Concepts
2. Setting Up the Environment
3. Writing Your First Java Program
4. Compiling and Running the Program
5. Common Practices
6. Best Practices
7. Conclusion
8. References

Fundamental Concepts

Java Platform

Java runs on the Java Virtual Machine (JVM), which allows Java programs to be platform - independent. Once you write a Java program, it can be compiled into bytecode (.class files). These bytecode files can then be run on any system with a compatible JVM.

Object - Oriented Programming

Java is an object - oriented language. This means that it organizes code around objects, which are instances of classes. A class is a blueprint that defines the properties and behaviors of an object. For example, a Car class could have properties like color and speed, and methods like accelerate() and brake().

Packages

Packages in Java are used to organize classes and interfaces. They help in avoiding naming conflicts and make the code more modular. For example, the java.util package contains many useful utility classes like ArrayList and HashMap.

Setting Up the Environment

Install the Java Development Kit (JDK)

The JDK is a software development environment used for developing Java applications. You can download the latest JDK from the official Oracle website or use an open - source alternative like OpenJDK.

Set Up the Environment Variables

After installing the JDK, you need to set up the JAVA_HOME environment variable, which points to the JDK installation directory. You also need to add the bin directory of the JDK to the PATH environment variable so that you can run Java commands from the command line.

On Windows:

1. Right - click on "This PC" and select "Properties".
2. Click on "Advanced system settings".
3. In the "System Properties" window, click on the "Environment Variables" button.
4. Under "System variables", click "New" and add a variable named "JAVA_HOME" with the value of your JDK installation directory.
5. Edit the "Path" variable and add `%JAVA_HOME%\bin` to it.

On Linux or macOS:

# Open the .bashrc or .zshrc file in a text editor
nano ~/.bashrc
# Add the following lines
export JAVA_HOME=/path/to/your/jdk
export PATH=$PATH:$JAVA_HOME/bin
# Save the file and source it
source ~/.bashrc

Writing Your First Java Program

Let’s write a simple “Hello, World!” Java program.

// This is a comment. Comments are used to explain the code and are ignored by the compiler.
// Define a class named HelloWorld
public class HelloWorld {
    // The main method is the entry point of a Java application
    public static void main(String[] args) {
        // Print "Hello, World!" to the console
        System.out.println("Hello, World!");
    }
}

Explanation of the Code

• public class HelloWorld: Defines a public class named HelloWorld. In Java, the name of the source file must match the name of the public class, so this code should be saved as HelloWorld.java.
• public static void main(String[] args): This is the main method of the Java application. It is the starting point of the program execution. The public keyword means that the method can be accessed from anywhere. static means that the method belongs to the class rather than an instance of the class. void means that the method does not return a value.
• System.out.println("Hello, World!");: This line prints the string “Hello, World!” to the console.

Compiling and Running the Program

Compile the Program

Open the command prompt or terminal, navigate to the directory where the HelloWorld.java file is saved, and run the following command:

javac HelloWorld.java

This command compiles the Java source code into bytecode. If there are no errors in the code, a HelloWorld.class file will be created in the same directory.

Run the Program

After compiling the program, you can run it using the following command:

java HelloWorld

You should see the output “Hello, World!” printed on the console.

Common Practices

Use Meaningful Names

When naming classes, methods, and variables, use meaningful names that describe their purpose. For example, instead of using a variable named x, use a more descriptive name like studentAge.

Add Comments

Comments are essential for making your code understandable. Add comments to explain complex logic, the purpose of a method, or any important details in your code.

Handle Exceptions

In Java, exceptions are used to handle errors and exceptional conditions. Use try - catch blocks to handle exceptions properly in your code. For example:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class ExceptionHandlingExample {
    public static void main(String[] args) {
        try {
            File myFile = new File("nonexistent.txt");
            Scanner scanner = new Scanner(myFile);
        } catch (FileNotFoundException e) {
            System.out.println("File not found: " + e.getMessage());
        }
    }
}

Best Practices

Follow the Java Coding Conventions

Oracle has defined a set of Java coding conventions that you should follow. These conventions include things like using camelCase for variable and method names, using PascalCase for class names, and indenting code properly.

Use Version Control

Use a version control system like Git to manage your code. Version control allows you to track changes to your code, collaborate with other developers, and easily revert to previous versions if needed.

Write Unit Tests

Unit testing is a software testing method where individual units of source code are tested to determine if they are fit for use. You can use testing frameworks like JUnit to write unit tests for your Java code.

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class CalculatorTest {
    @Test
    public void testAddition() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result);
    }
}

class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

Conclusion

Building your first Java application is a significant step in your software development journey. By understanding the fundamental concepts, setting up the environment correctly, writing and running your first program, and following common and best practices, you can create robust and maintainable Java applications. As you continue to learn and practice, you’ll be able to explore more advanced Java features and build more complex applications.

References

• Oracle Java Documentation: https://docs.oracle.com/javase/8/docs/
• OpenJDK: https://openjdk.java.net/
• JUnit: https://junit.org/junit5/