Java Dead Code Confusion: Is My Sir Right?

Is My Sir Right?

📝 Day 2 – Java Dead Code Confusion: Is My Sir Right?

Today I was testing some simple Java conditionals, and something strange happened...

My sir said the code I wrote would throw a "dead code" error. But when I ran it — it worked perfectly fine. So, I dug deeper to see who’s right and what's really happening under the hood.

💡 What is Dead Code?

Dead code refers to code that will never execute, no matter what.

For example:

if (false) {
   // This code will never run
}

💻 My Code:

class PositiveCheck {
    public static void main(String[] args) {
        int num = 5;
        if (false) {
            System.out.println("Positive Number");
        }
    }
}

🧠 What My Sir Said:

He told me this will throw an error because the code inside the if (false) block is dead code (since false is always false).

But...

🤔 What Actually Happened:

It ran without any error!

So I got confused — was my teacher wrong? Or is there something else happening here?

🔍 What’s Really Going On?

Java does detect unreachable code (dead code) sometimes, but not always. It depends on:

The Java version
The compiler
The IDE settings

⚠️ Example That May Cause Dead Code Error:

public class Demo {
    public static void main(String[] args) {
        if (false) {
            System.out.println("Dead Code"); // ❌ Error: unreachable statement
        }
    }
}

✅ When You See the Error:

Using older Java versions
Running with javac from terminal (javac Demo.java)
Compiler strictness is high
IDE like Eclipse may warn only if settings are set to show such errors

✅ When You Don’t See the Error:

Your IDE (like IntelliJ or Eclipse) is more lenient by default
Java compiler may optimize it silently
Some versions just ignore unreachable if (false) if it doesn’t affect program logic

📋 Summary Table

Code	Dead Code Error?	Why
`if (true)`	❌ No	Runs normally
`if (false)`	❓ Maybe	Depends on compiler version
`while(false)`	✅ Yes	Clearly unreachable loop
Code after `return`	✅ Yes	Not reachable after return
Unused variable	❌ No	Just a warning, not error

🧪 Try it Yourself

You can try this in a strict online compiler:

👉 Try on JDoodle or

👉 Use terminal:

javac Demo.java

You might get:

error: unreachable statement
        System.out.println("Dead Code");

🧠 So... Is My Sir Right?

✅ Yes, technically he is right in principle.

🚫 But, in your specific Java version or environment, Java did not treat the if(false) block as a compile-time error — so you’re also right to be confused!