JAVA — CHAPTER 1

Hardware units

• Input (keyboard, mic, sensors)
• Output (screen, speaker)
• Memory (fast, volatile)
• Secondary storage (SSD/disk)
• CPU + GPU (arithmetic/logic + parallel math)

Language levels

• Machine language — pure 0s & 1s
• Assembly — mnemonics (ADD, MOV)
• High-level (Java, Python) — English-like
• Compilers/interpreters translate high-level → machine code

Programming paradigm

• Procedural — step-by-step instructions
• Object-oriented — models real-world "things"
• Java is class-based, object-oriented

Key idea

A computer is a general-purpose machine — hardware is the physical device, software (programs) tells it what to do. Java programs are software that run on any device with a JVM.

Origins

• Created by James Gosling at Sun Microsystems (1991, "Project Green")
• Now owned & developed by Oracle
• One of the most used languages for apps, web back-ends, Android

Core traits

• WORA — Write Once, Run Anywhere
• Compiled to bytecode, run by the JVM
• Automatic memory management (garbage collection)
• Strongly typed & security-checked at multiple stages

Java editions

• Java SE — Standard Edition (desktop/console apps)
• Jakarta/Java EE — enterprise, web servers
• Java ME — embedded/small devices

Core vocabulary

• Class — blueprint (e.g., Car)
• Object — an instance built from the class
• Attributes — data an object carries (color, speed)
• Methods — behaviors an object can perform (accelerate())

Four pillars

• Encapsulation — bundle data + behavior, hide internals
• Inheritance — new class reuses/extends an existing one
• Polymorphism — one method call, many object-specific behaviors
• Abstraction — expose what an object does, not how

Java API

Thousands of prebuilt classes (java.lang, java.util, java.io…) so you don't reinvent common functionality.

Why reuse?

• Faster development
• Fewer bugs — code is already tested
• Consistent, well-documented behavior

Build tools & repos

• Maven / Gradle — manage project dependencies
• Open-source libs downloaded from public repositories
• Community libraries extend what the core API offers

Internet & Web

Global network of networks; the Web is the system of linked pages/apps that run over it.

Cloud computing

Storage & computing power delivered as a service over the internet instead of on local machines.

Internet of Things

Everyday devices (thermostats, wearables, cars) connected and exchanging data online.

Metaverse

Persistent, shared virtual/AR spaces where people interact as digital avatars.

Big Data — the 4 V's

• Volume — massive amounts of data
• Velocity — generated/processed at high speed
• Variety — structured, text, images, video…
• Veracity — trustworthiness/quality of the data

What it is

AI models (LLMs) trained on huge text/code corpora that generate new, original content — text, explanations, and code — in response to a prompt.

How this book uses it

• Generate starter code & explanations while you learn syntax
• Compare your own solution to an AI-generated one
• Practice "prompt engineering" — asking clear, specific questions

Cautions

• AI output can be wrong — always test and verify
• Understand the code before using it — don't copy blindly
• Data privacy: don't paste confidential code into public tools