Thread: What will the compiler remove from the code?

Hi there.

Edit: I googled some more and found out, that the java compiler does almost no optimization at all.
Java relies on the JIT to do all kinds of optimization.
But there are 3rd party applications to optimize the byte code generated by a compiler a little more.

I have a quick question: How good is the compiler at noticing dead code and removing it before creating byte-code?
Lets assume I have the following code:

public class ImportantClass {
 
	private static final boolean DEBUG = false;
 
	public void importantTask() {
		doStuff();
		debug("This is an important message!");
	}
 
	private void debug(String text) {
		if (DEBUG) {
			System.out.println(text);
		}
	}
 
	private void doStuff() {
		// This is very complicated stuff right here!
	}
 
}

Would the compiler remove the call to "debug"?
Would the compiler remove the method "debug(String)"?
If it would not, is there some simple way for me to implement a conditional output which is removed from the final release?

I am working with Eclipse Juno SR2 at the moment if this is important.

Thank you very much.

Unreachable statements cause a compiler error.

Empty blocks, like a while( true ) block with nothing in it, are removed per the compiler's optimization logic.

In your example above, I don't believe the call to debug() would be removed, because debug() contains logic that would have to be evaluated, but I can't point to a reference that confirms that, and I could be wrong.

And, No, the IDE you're using is not important or even relevant.

Originally Posted by GregBrannon

Unreachable statements cause a compiler error.

Empty blocks, like a while( true ) block with nothing in it, are removed per the compiler's optimization logic.

In your example above, I don't believe the call to debug() would be removed, because debug() contains logic that would have to be evaluated, but I can't point to a reference that confirms that, and I could be wrong.

I was just thinking that, since DEBUG is a final variable and set to false, the compile might realize that the entire if-block can be removed.
And then, since the method "debug(...)" doesnt contain anything anymore (after the if-block has been removed) the entire method might get removed.
And if the method is removed then obviously the call to the method would need to be removed as well.

I know that some fancy C compilers can do stuff like this.

Originally Posted by GregBrannon

And, No, the IDE you're using is not important or even relevant.

If I am not mistaken there are different Java-compilers out there. So perhaps a different IDE might use a different compiler. I dont really know, but thanks for clarifying.

Edit: After googling a bit about it I read on wikipedia, that eclipse has its own java compiler. Whether the eclipse version I use actually uses this different java compiler is not known to me.
Source: http://en.wikipedia.org/wiki/Java_compiler

Okay, thank you very much.
I have, however, found several programs which optimize the byte-code after compilation and claim to fix problems like these.