Java - Introduction

Key Concepts

• JVM: The Java Virtual Machine executes compiled bytecode.
• JRE: The Java Runtime Environment (JVM + standard libraries) to run apps.
• JDK: The Java Development Kit (JRE + compilers/tools) to build apps.
• WORA: Write Once, Run Anywhere—portable bytecode across platforms.
• LTS releases: Long-Term Support versions (e.g., 8, 11, 17, 21) are common in production.

Hello, World

Save this as Hello.java:

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

Compile and run:

# compile
javac Hello.java
# run
java Hello

Typical Use Cases

• Enterprise backends (REST, microservices)
• Android applications (Kotlin and Java interop)
• Big data (Hadoop ecosystem), stream processing
• Trading systems and low-latency services

Next Steps

1. Install a modern JDK and IDE/tooling.
2. Learn syntax, variables, control flow.
3. Dive into OOP: classes, interfaces, inheritance.
4. Master collections, generics, exceptions.
5. Explore lambdas, streams, and concurrency.