Is Java Compiled or Interpreted? Let’s Clear the Confusion!

Ramesh Fadatare

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Mar 21, 2025

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When you’re just starting with Java, one question pops up often:

🤔 “Is Java a compiled language or an interpreted one?”

It’s a great question — and the truth is, Java is both! Let’s understand this step-by-step in a way that’s clear, simple, and beginner-friendly.

📌 What Happens When You Run a Java Program?

Let’s say you have the following Java code:

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

You run this using:

javac HelloWorld.java
java HelloWorld

What actually happens behind the scenes? Let’s break it down:

1️⃣ Compilation Phase (Source Code → Bytecode)

Java source files (.java) are first compiled by the Java compiler (javac) into something called bytecode (.class files).

🧾 Bytecode is a low-level, platform-independent code that the JVM can understand — but your computer cannot run it directly.

javac HelloWorld.java   →   HelloWorld.class

✅ This is the compiled part of Java.

Bytecode is NOT machine code. It’s an intermediate representation.

2️⃣ Execution Phase (Bytecode → Machine Code)

The compiled bytecode is then passed to the Java Virtual Machine (JVM).

Here’s where Java becomes interpreted.

➡️ The JVM reads the bytecode line-by-line and translates it into machine-specific instructions that your OS can execute.

So yes — the JVM interprets the bytecode during runtime.

3️⃣ 🚀 JIT Compiler: Best of Both Worlds

To make execution faster, the JVM also uses a JIT (Just-In-Time) compiler.

🛠️ What does JIT do?

• It watches which parts of your code are used a lot.
• Then it compiles those parts into native machine code at runtime.
• So next time, the JVM doesn’t need to interpret them again — improving performance.