Introduction to Java Programming

What is Java programming?

Java is a programming language used to write instructions that a computer can execute. Java uses static types, classes, methods, automatic memory management, and exception handling to help developers create structured and maintainable applications.

How does Java work?

1. You write source code in a .java file.
2. The Java compiler, javac, checks the code and creates bytecode in a .class file.
3. The JVM loads, verifies, and executes the bytecode on the computer.

Your first Java program

The following program prints a message to the console.

public class HelloJava {
    public static void main(String[] args) {
        System.out.println("Hello, Java!");
    }
}

Output

Hello, Java!

How the program works

• public class HelloJava declares a class named HelloJava. In a traditional Java source file, executable methods and fields are declared inside a class.
• public static void main(String[] args) is the entry point used to start this program:
  • public: The method is accessible to the Java launcher.
  • static: The JVM can invoke main() without first creating a HelloJava object.
  • void: The method does not return a value.
  • main: The conventional entry-point method name used by the Java launcher.
  • String[] args: An array containing command-line arguments passed when the program starts.
• System.out.println() prints text followed by a new line.

Brief history of Java

Java emerged from Sun Microsystems’ Green Project in 1991. The development team was led by James Gosling and initially focused on portable software for consumer electronic devices.

The language was known as Oak during early development. It was later renamed Java after trademark concerns with the Oak name.

Java was publicly introduced in 1995, and JDK 1.0 was released in January 1996.

Why learn Java?

• Beginner-friendly: clean, readable C-style syntax with no manual memory management.
• High demand: consistently among the top languages requested by software employers worldwide.
• Enterprise standard: the backbone of banking, e-commerce, and large-scale backend systems.
• Strong OOP foundation: teaches object-oriented thinking that transfers to many other languages.
• Huge ecosystem: mature libraries, frameworks (Spring, Hibernate), tooling, and a vast community.

Where is Java used?

• Backend services and enterprise applications
• Banking, payment, and transaction-processing systems
• Android-related applications and shared mobile libraries
• Desktop tools, IDEs, build systems, and developer utilities
• Cloud services, messaging systems, and distributed applications

Java Editions

Java is packaged into different editions, each targeting a specific type of application:

Common beginner mistakes

System.out.println("Hello")

System.out.println("Hello");