Compiler

A compiler is a program that translates source code written in a high-level language (like Java, C, or Kotlin) into another form — usually:

• Machine code (for direct execution by the CPU)
  or

• Intermediate code (like Java bytecode, which runs on a VM)

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🔸 What a Compiler Actually Does

It analyzes your code and performs multiple stages:

Stage	What It Does
Lexical Analysis	Breaks code into tokens (keywords, variables, etc.)
Syntax Analysis	Checks grammar (e.g., matching {}, method structure)
Semantic Analysis	Validates type safety, variable usage, etc.
Intermediate Code Generation	Converts code to bytecode or IR
Optimization	Improves performance (e.g., removes dead code)
Code Generation	Outputs bytecode or native machine code

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🔹 Java Compiler (javac)

For Java, the compiler:

• Takes .java files

• Produces .class files containing bytecode

• That bytecode runs on the JVM, not directly on the CPU

javac MyApp.java   # Compile to bytecode
java MyApp         # JVM runs it

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🔸 Compiler vs Interpreter

Feature	Compiler	Interpreter
Output	Machine code or bytecode	Executes code line by line
Speed	Faster after compilation	Slower due to real-time parsing
Java Uses	javac for compilation → JVM runs/interprets	JVM includes both interpreter & JIT compiler

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✅ TL;DR

A compiler converts source code into lower-level code (machine code or bytecode), so it can be executed efficiently by hardware or a virtual machine.

Let me know if you want to walk through how javac translates a specific Java snippet into bytecode.