Introduction to Java Programming

What is Java programming?

Java was designed to let developers write structured programs that can run on systems with a compatible JVM. Java uses static types, classes, methods, automatic memory management, and exception handling to support maintainable applications.

How does Java work?

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

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 Java, all code must be inside a class.
• public static void main(String[] args) is the entry point used to start this program. Here's a breakdown:
  • public: The method is accessible from other classes, including the Java launcher that invokes main().
  • static: The JVM can invoke main() without first creating an instance of the HelloJava class.
  • void: The method does not return a value.
  • main: The conventional entry-point method name used by the Java launcher.
  • String[] args: An array of strings that stores command-line arguments passed to the program when it 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?

• Structured learning path: Java introduces variables, conditions, loops, methods, classes, exceptions, and collections in a systematic way.
• Broad professional use: Java is used across enterprise software, backend systems, developer tools, and Android-related codebases.
• Widely used in enterprise applications.
• Excellent support for object-oriented programming.
• Large community and learning resources.
• Platform Independent: Java follows the principle of WORA — Write Once, Run Anywhere.

Where is Java used?

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

Common beginner mistakes

System.out.println("Hello") // Missing semicolon!

System.out.println("Hello");