Introduction to Java Programming

Java evolution, features, JVM/JRE/JDK, basic syntax, and compilation workflow.

Evolution of Java

Java was developed by James Gosling at Sun Microsystems in 1995. It was designed to be platform-independent, following the principle of “Write Once, Run Anywhere” (WORA).

Java Features

Java is known for being:

• Simple — Clean syntax derived from C/C++ with automatic memory management.
• Object-Oriented — Everything revolves around classes and objects.
• Platform-Independent — Bytecode runs on any platform with a JVM.
• Robust — Strong type checking, exception handling, and garbage collection.
• Secure — No explicit pointers, bytecode verification, and a security manager.
• Multithreaded — Built-in support for concurrent programming.
• High-Performance — Just-In-Time (JIT) compilation.
• Distributed — Support for networking via RMI and EJB.
• Dynamic — Runtime class loading and reflection.
• Architecture-Neutral — Fixed-size primitive types across platforms.

Java Workflow: JVM, JRE, JDK

• JDK (Java Development Kit) — Full development environment including compiler (javac), debugger, and tools.
• JRE (Java Runtime Environment) — Runtime libraries and the JVM needed to run Java programs.
• JVM (Java Virtual Machine) — Executes Java bytecode on any platform.

Basic Syntax

A Java program consists of classes, methods, and statements:

• The main method is the entry point: public static void main(String[] args).
• Comments can be single-line (//), multi-line (/* */), or Javadoc (/** */).
• Identifiers must start with a letter, underscore, or dollar sign.

Compilation and Execution

javac HelloWorld.java   # Compile to bytecode
java HelloWorld         # Run with JVM

Example

// HelloWorld.java
// This is a simple Java program that prints "Hello, World!" to the console.

public class HelloWorld {
	// The main method is the entry point of any Java program.
	public static void main(String[] args) {
		// Prints Hello, World! to the console.
		System.out.println("Hello, World!");
	}
}

Full source: examples/01-introduction/HelloWorld.java

User Input

Java provides the Scanner class for reading user input:

import java.util.Scanner;

Scanner sc = new Scanner(System.in);
String name = sc.nextLine();
int age = sc.nextInt();