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Java Capability

13 replies on 1 page. Most recent reply: Dec 10, 2004 2:04 AM by Vincent O'Sullivan

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Flat View: This topic has 13 replies on 1 page

Vikram V Hegde

Posts: 1
Nickname: vikram81
Registered: Aug, 2004

Java Capability

Posted: Dec 2, 2004 11:30 PM

I have a question about java Please suggest any relavent answers,

Is there any option in java, to neglect a block of java code while complilation so that it(that neglected block of code) would not be included in generate Byte code/Class file? [ NOTE: Please ignore the commentting operator (/**/ or //) as solution ]

Thanks in Advance,
Vikram Vishwanath

Amol Brid

Posts: 43
Nickname: amolbrid
Registered: Feb, 2004

Re: Java Capability

Posted: Dec 3, 2004 2:09 AM

Hi Vikram,

This is a strange requirement.
Why u want to do this?

Amol Brid.

toure

Posts: 2
Nickname: petert17
Registered: Nov, 2004

Re: Java Capability

Posted: Dec 4, 2004 12:56 PM

please let me know when you got the solution
that's would fascinating!

stephen handley

Posts: 3
Nickname: one2one3
Registered: Dec, 2004

Re: Java Capability

Posted: Dec 4, 2004 10:24 PM

would a conditionally returned inner class work?
public static YourClass classReturner (boolean doit) {
if (doit)
return new YourClass() {
//your class body with desired non compiled block of code
};
else
return null;
}

i'm guessing even if doit was declared as
final boolean doit = FALSE;
it would still compile? i'm not sure though.

Matt Gerrans

Posts: 1153
Nickname: matt
Registered: Feb, 2002

Re: Java Capability

Posted: Dec 5, 2004 7:02 PM

Sure; just write that block of code in the Whitespace programming language. See http://compsoc.dur.ac.uk/whitespace/

Vincent O'Sullivan

Posts: 724
Nickname: vincent
Registered: Nov, 2002

Re: Java Capability

Posted: Dec 6, 2004 4:35 AM

Yes. If the condition in a conditional statement can be resolved at compile time then the 'false' part of the statement will not be compiled. For instance:

final String state = "live";
 
if {state == "live"}
{
    // Do live stuff.
    // e.g. Connect to the live database.
}
else
{
    // Do test stuff.
    // e.g. Connect to the test database.
}

This would compile to (the bytecode equivalent of):

String state = "live";
 
// Do live stuff.
// e.g. Connect to the live database.

Vince.

sandeep

Posts: 2
Nickname: sandeepgrp
Registered: Dec, 2004

Re: Java Capability

Posted: Dec 6, 2004 8:46 PM

>final String state = "live";

>if {state == "live"}
>{
> // Do live stuff.
> // e.g. Connect to the live database.
>}
>else
>{
> // Do test stuff.
> // e.g. Connect to the test database.
>}

>This would compile to (the bytecode equivalent of):
>String state = "live";

>// Do live stuff.
>// e.g. Connect to the live database.

but javac compile all the code
as if we make an error in else part it give error at that point so java compile all the code (except commented)

Vincent O'Sullivan

Posts: 724
Nickname: vincent
Registered: Nov, 2002

Re: Java Capability

Posted: Dec 7, 2004 2:36 AM

That doesn't really prove anything. You would not expect code that contains errors to compile...and it doesn't.

Matthias Neumair

Posts: 660
Nickname: neumi
Registered: Sep, 2003

Re: Java Capability

Posted: Dec 7, 2004 5:36 AM

The question was not about the execution, but about how to write something without getting it compiled.

As far as I know that just isn't possible, as long as you don't use the comment option.

Vincent O'Sullivan

Posts: 724
Nickname: vincent
Registered: Nov, 2002

Re: Java Capability

Posted: Dec 8, 2004 12:17 AM

> The question was not about the execution, but about how to
> write something without getting it compiled.

I see your point.

Nevertheless, the code isn't compiled (into the class file) but, because the 'unwanted' code is not a comment, the compiler still needs to check it for semantic correctness. If errors are found the compiler can no longer assume it has a block of unwanted code. It just sees the errors.

Either way the unwanted code does not make it into the class file.

V.

Matthias Neumair

Posts: 660
Nickname: neumi
Registered: Sep, 2003

Re: Java Capability

Posted: Dec 9, 2004 12:41 AM

Unreachable code doesn't get stored into the .class file?

I didn't know that.

Vincent O'Sullivan

Posts: 724
Nickname: vincent
Registered: Nov, 2002

Re: Java Capability

Posted: Dec 9, 2004 2:12 AM

> Unreachable code doesn't get stored into the .class file?
>
> I didn't know that.

Nor did I. That'll be why that wasn't what I said.

Matt Gerrans

Posts: 1153
Nickname: matt
Registered: Feb, 2002

Re: Java Capability

Posted: Dec 9, 2004 11:18 AM

But that is the correct conclusion, isn't it? If the compiler can determine at compile time that a chunk of code is unreachable, then it won't appear in the class file.

Vincent O'Sullivan

Posts: 724
Nickname: vincent
Registered: Nov, 2002

Re: Java Capability

Posted: Dec 10, 2004 2:04 AM

> But that is the correct conclusion, isn't it?

Maybe, maybe not. It's a reasonable hypothesis but not necessarily a correct conclusion since it involves making a generalisation from a specific case.

For myself, I know that it happens if an if statemant can be resolved at compile time. I don't know if the same happens for all unreachable code.

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