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Does a way exist to instruct the Java compiler to compile code only
if a certain version of Java is supported? For example, I may want to
measure with milliseconds in Java 1.4 or nanoseconds if I'm running in
Java 5.

import java.io.IOException;

public class JVMLoadTimeRunner {

public static void main(String[] args) {

long start = System.currentTimeMillis(); // only compile this line
in Java 1.4
//long start = System.nanoTime(); // only compile this line in Java
5

try {
Process newP = Runtime.getRuntime().exec( cmd );
newP.waitFor();
long end = System.currentTimeMillis();
System.out.println( "Process Execution took " + (float)(end-start)/
1000F + " seconds" );
// Java 5
// System.out.println( "Process Execution took " + (float)(end-
start)/1000000000F + " seconds" );
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
System.out.println( "Process wait threw an Exception" );
e.printStackTrace();
}
}
}

timjowers wrote:
>
> Does a way exist to instruct the Java compiler to compile code only
> if a certain version of Java is supported? For example, I may want to
> measure with milliseconds in Java 1.4 or nanoseconds if I'm running in
> Java 5.
>

<http://www.google.com/search?q=java+conditional+compilation&hl=en&start= 10&sa=N>

On Mon, 02 Jul 2007 18:11:21 -0000, timjowers <>
wrote, quoted or indirectly quoted someone who said :

> long start = System.currentTimeMillis(); // only compile this line
>in Java 1.4
> //long start = System.nanoTime(); // only compile this line in Java

You can look at a system property at run time and use that in an if.

java.specification.version = 1.6

java.version = 1.6.0_01

java.vm.version = 1.6.0_01-b06

see http://mindprod.com/jgloss/properties.html
--
Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com

timjowers wrote:
> Does a way exist to instruct the Java compiler to compile code only
> if a certain version of Java is supported? For example, I may want to
> measure with milliseconds in Java 1.4 or nanoseconds if I'm running in
> Java 5.

Not as you can in C/C++.

You could use an external preprocessor.

But I would drop the idea.

Arne

Roedy Green wrote:
> On Mon, 02 Jul 2007 18:11:21 -0000, timjowers <>
> wrote, quoted or indirectly quoted someone who said :
>
>> long start = System.currentTimeMillis(); // only compile this line
>> in Java 1.4
>> //long start = System.nanoTime(); // only compile this line in Java
>
> You can look at a system property at run time and use that in an if.
>
> java.specification.version = 1.6
>
> java.version = 1.6.0_01
>
> java.vm.version = 1.6.0_01-b06

That will not help at compilation.

Arne

FWIW, I decided on the exploit of compiler optimization. The technique
is to create unreachable code with as if(false) and put your Java 5
code there. Make that block reachable to compile in Java 5. E.g.

boolean JAVA_5_PLUS = false;
// Java by design lacks conditional compilation so various
workarounds
// are to comment out code, use a custom preprocessor (see Munge
from the Swing team),
// or use if( false ) or such blocks (which are normally not
compiled due to optimizing them out.)
if( JAVA_5_PLUS )
start = System.nanoTime();
else
start = System.currentTimeMillis();
TimJowers

timjowers wrote:
> FWIW, I decided on the exploit of compiler optimization. The technique
> is to create unreachable code with as if(false) and put your Java 5
> code there. Make that block reachable to compile in Java 5. E.g.
>
> boolean JAVA_5_PLUS = false;
> // Java by design lacks conditional compilation so various
> workarounds
> // are to comment out code, use a custom preprocessor (see Munge
> from the Swing team),
> // or use if( false ) or such blocks (which are normally not
> compiled due to optimizing them out.)
> if( JAVA_5_PLUS )
> start = System.nanoTime();
> else
> start = System.currentTimeMillis();

I am very surprised if that compiles with the 1.4 compiler.

Compile with 1.5 and run on 1.4 should work.

Arne

[heyjude]

There is an external tool called wwyt which does just that. It's a Windows command line tool, it pre-process your Java source files, which are embedded with conditional compile directives (like #if, #else, ...). You then let compiler compile these converted files and get the .class files you want. After compilation, you should run wwyt tool again so that the converted files are restored back to their original status.

URL is this: adarian dot com slash wwyt

Hope this helps.