Introduction to Java

## Learning Objectives - Understand Java history and platform - Set up Java development environment - Write and run your first Java program - Understand Java syntax basics ## What is Java? Java is a high-level, object-oriented programming language developed by Sun Microsystems (now Oracle). ```java public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } } ``` ## Java Platform ### Key Features - **Write Once, Run Anywhere** - Java code compiles to bytecode - **Object-Oriented** - Everything except primitives is an object - **Strongly Typed** - Must declare variable types - **Automatic Memory Management** - Garbage collection ### Platform Components | Component | Description | |-----------|-------------| | JDK | Java Development Kit | | JRE | Java Runtime Environment | | JVM | Java Virtual Machine | ## Installing Java ### Download Get JDK from or OpenJDK from ### Verify Installation ```bash java --version javac --version ``` ## Your First Program ### File: HelloWorld.java ```java public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); } } ``` ### Compile and Run ```bash javac HelloWorld.java # Creates HelloWorld.class java HelloWorld # Runs the program ``` ## Java Program Structure ```java public class ClassName { // Class declaration public static void main(String[] args) { // Main method // Statements go here } } ``` ### Components 1. **Class**: Template for creating objects 2. **Main method**: Entry point of the program 3. **Statements**: Commands to execute ## Comments ```java // Single-line comment /* * Multi-line comment */ /** * Documentation comment (Javadoc) */ ``` ## The main Method ```java public static void main(String[] args) { // args: command-line arguments for (String arg : args) { System.out.println(arg); } } ``` ## System Output ```java // Print with newline System.out.println("Hello"); // Print without newline System.out.print("Hello "); System.out.print("World"); // Print formatted (Java 15+) System.out.printf("Name: %s, Age: %d%n", "Alice", 30); ``` ## Command Line Arguments ### Hello.java ```java public class Hello { public static void main(String[] args) { if (args.length > 0) { System.out.println("Hello, " + args[0]); } else { System.out.println("Hello, World!"); } } } ``` ```bash javac Hello.java java Hello Alice # Output: Hello, Alice ``` ## IDEs ### Popular IDEs - IntelliJ IDEA (recommended) - Eclipse - VS Code with Java extension - NetBeans ## Java Versions ```bash java --version # Check installed version ``` | Version | Year | Feature | |---------|------|---------| | Java 8 | 2014 | Lambdas, Streams | | Java 11 | 2018 | LTS, var | | Java 17 | 2021 | LTS, Sealed Classes | | Java 21 | 2023 | LTS, Virtual Threads | ## Summary - Java is platform-independent through bytecode - JDK includes compiler and runtime - Every Java program has a class with main method - `javac` compiles `.java` to `.class` - `java` runs the bytecode - Comments: `//`, `/* */`, `/** */`