Chapter 2: Java Overview & Memory Model

Java is a mature, high-performance, object-oriented language designed with the "Write Once, Run Anywhere" (WORA) philosophy. Understanding its runtime architecture, execution pipeline, type system, root Object lifecycle contracts, and the Java Memory Model (JMM) is foundational for modern backend engineering.

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🧭 Subtopics & Curriculum

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Runtime Architecture2.1

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2.1 JDK vs JRE vs JVM

• 1. Architectural Relationship
  • Breakdown:
• 2. "Write Once, Run Anywhere" (WORA)

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Execution Engine2.2

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2.2 Bytecode & Execution Engine

• 1. Class Loading Mechanism (The 3 Phases)
• 2. The Execution Engine: Interpreter vs JIT Compiler

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Type System2.3

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2.3 Data Types, Primitives & Wrappers

• 1. The 8 Primitive Types in Java
• 2. Autoboxing & The Integer Cache Trap
  • The Integer Cache Gotcha (-128 to 127)

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Logic & Control Flow2.4

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2.4 Operators & Modern Control Flow

• 1. Short-Circuit Logical Operators
• 2. Modern Switch Expressions (Java 14+)
• 3. Pattern Matching for Switch (Java 21 LTS)

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Call Semantics2.5

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2.5 Methods & Pass-by-Value Semantics

• 1. The Definitive Proof: References are Passed by Value
  • Memory Trace:
• 2. Varargs (Variable-Length Arguments)

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Modern Features2.6

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2.6 Java Evolution & LTS Features

• 1. Landmark LTS Versions Overview
• 2. Core Breakthroughs in Recent Java
  • A. Records (Java 16)
  • B. Sealed Classes (Java 17)
  • C. Sequenced Collections (Java 21)
  • D. Virtual Threads (Java 21 LTS - Project Loom)

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Root Hierarchy2.7

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2.7 java.lang.Object Core Methods

• 1. Summary of All 11 Methods
• 2. Shallow Copy vs Deep Copy with clone()

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Object Equality2.8

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2.8 The equals() & hashCode() Contract

• 1. The Mathematical Contract
• 2. What Breaks If You Override equals() Without hashCode()?
  • The Catastrophic Bug:
• 3. Idiomatic Implementation with java.util.Objects

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Memory Layout2.9

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2.9 JVM Memory Model Architecture

• 1. JVM Runtime Data Areas Overview
• 2. Deep Dive: Memory Regions
  • A. Java Heap
  • B. Thread Stack (JVM Stack)
  • C. Metaspace (Native Memory, Java 8+)
  • D. Program Counter (PC) Register

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Concurrency & JMM2.10

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2.10 JMM Concurrency, Volatile & Memory Barriers

• 1. The Core Problem: Hardware Caches & Reordering
• 2. The volatile Keyword
• 3. The "Happens-Before" Relationship

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