X'inhu d-differenza bejn JVM, JRE u JDK?

Question

Accepted Answer

Dawn it-tliet akronimu jiddeskrivu l-istrati mħabbka tal-pjattaforma Java. Il-mod l-aktar sempliċi biex tiftakra: **JDK fih JRE, li fih JVM** — kull wieħed iżżid kapaċitajiet lil dak li jinsab ġewwa tiegħu.

## Għaliex dan importanti

Il-fahim tad-differenza JVM/JRE/JDK jikkjarifika l-arkitettura tal-pjattaforma Java u jirrispondi għall-mistoqsija prattika: i-sviluppaturi jinstallaw il-**JDK** (biex jikkompilaw u jibnu), il-**JVM** realment jesegwixxi bytecode u jippermettu l-indipendenza tal-pjattaforma + garbage collection, u l-**JRE** storikament ipprovdiet biss il-runtime biex tesegwixxi l-applikazzjonijiet.

Dan il-mudell stratifikat jispjega kif kodiċi Java jmur mis-sors għal programm li qed jatħaddem, għaliex WORA jaħdem (l-istrat JVM), u x'għandek tinstalla għal kompitu partikolari — għarfien fundamentali biex tistabbilixxi u tikkunsidra kwalunkwe ambjent Java.

## In-nesting

```text
┌─────────────────────────── JDK (Development Kit) ───────────────────┐
│  javac (compiler), debugger, javadoc, jar, other dev tools          │
│  ┌─────────────────────── JRE (Runtime Environment) ─────────────┐  │
│  │  Java class libraries (standard API: java.util, java.io, ...)  │  │
│  │  ┌──────────────────── JVM (Virtual Machine) ───────────────┐  │  │
│  │  │  Executes bytecode, JIT compilation, garbage collection   │  │  │
│  │  └───────────────────────────────────────────────────────────┘  │  │
│  └─────────────────────────────────────────────────────────────────┘  │
└────────────────────────────────────────────────────────────────────────┘
```

## JVM — Java Virtual Machine (il-magna runtime)

```text
Executes the bytecode. Responsibilities:
  ✓ Loads .class files, verifies bytecode
  ✓ Interprets / JIT-compiles bytecode to native machine code
  ✓ Manages memory & garbage collection
It's the layer that makes "write once, run anywhere" work — platform-specific
JVMs run the SAME bytecode.
```

## JRE — Java Runtime Environment (biex TMEXXI l-apps)

```text
JVM + the standard class libraries (the built-in API your code calls).
What you need to RUN a Java application — but NOT to compile one.
```

## JDK — Java Development Kit (biex TIBNI l-apps)

```text
JRE + development tools:
  javac   — the compiler (.java → .class bytecode)
  jdb     — debugger
  javadoc — documentation generator
  jar     — packaging tool
What a DEVELOPER needs to write, compile, and build Java programs.
```

## Liema wieħed għandek bżonn?

```text
Writing/compiling Java code  → JDK (it includes everything)
Only running a Java app      → JRE was historically enough
  (modern Java often bundles the runtime; JRE is less separately distributed now)
```