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Any similar technique like C's #ifdef in Java?

5 replies on 1 page. Most recent reply: Aug 14, 2003 4:25 PM by Matt Gerrans

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Kenneth Rajkumar

Posts: 1
Nickname: aalker123
Registered: Aug, 2003

Any similar technique like C's #ifdef in Java?

Posted: Aug 13, 2003 12:16 AM

Hello all,

I am looking for a similar technique of C's #ifdef in Java (J2ME)? Any idea or tips or help?

Thanks.

David

Posts: 150
Nickname: archangel
Registered: Jul, 2003

Re: Any similar technique like C's #ifdef in Java?

Posted: Aug 13, 2003 1:52 AM

There is no pre-processor in Java.

If I was you, I'd use the System Properties to set flags such as those for which you would use a pre-processor.

Slager .

Posts: 16
Nickname: slager
Registered: May, 2003

Re: Any similar technique like C's #ifdef in Java?

Posted: Aug 14, 2003 12:41 AM

Indeed there is no preprocessor.

You can use this construct in some situations :

static final boolean DEBUG = true/false;
if(DEBUG) { ... }

If DEBUG is set to false, the compiler will leave out the entire if block, because it is declared final.

David

Posts: 150
Nickname: archangel
Registered: Jul, 2003

Re: Any similar technique like C's #ifdef in Java?

Posted: Aug 14, 2003 12:51 AM

Do you know that for sure?

Slager .

Posts: 16
Nickname: slager
Registered: May, 2003

Re: Any similar technique like C's #ifdef in Java?

Posted: Aug 14, 2003 12:58 AM

Yup, at least with sun's compiler.

The following class :


public class Optimize {
	public static final boolean DEBUG = false;
	
	public Optimize() {
		if(DEBUG) {
			System.out.println("Test");
		}
	}
	
}

Compiled with DEBUG=true:


Method Optimize()
   0 aload_0
   1 invokespecial #1 <Method java.lang.Object()>
   4 getstatic #2 <Field java.io.PrintStream out>
   7 ldc #3 <String "Test">
   9 invokevirtual #4 <Method void println(java.lang.String)>
  12 return

And compiled with DEBUG=false:


Method Optimize()
   0 aload_0
   1 invokespecial #1 <Method java.lang.Object()>
   4 return

Matt Gerrans

Posts: 1153
Nickname: matt
Registered: Feb, 2002

Re: Any similar technique like C's #ifdef in Java?

Posted: Aug 14, 2003 4:25 PM

In conjunction with this, you could write a simple script that goes through all the java files in your project and modifies the line matching something like "^\s*public static final boolean DEBUG = (false|true);\s*$" (I'm not a regualar expression guru, so it can probably be improved upon) to either true or false as appropriate (debug vs. release).

<mount object="soapbox">Incidentally, I think the knowledge of conditionally-compiled code makes people a bit too anal retentive on this issue. That is, using a system property as in a previous suggestion is probably acceptible -- and more flexible -- in most cases. Once people become aware of the idea that a trace or log message can be conditionally compiled out, they get this notion that if it doesn't, it will have some huge impact on the performance of the program. This is usually not the case. In the small number of cases where it is, it can be specifically addressed.</mount>

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