Import efficiency

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Crouchez - 17 Dec 2007 23:09 GMT

Is importing a class directly ie.

import java.io.InputStream

more efficient than

import java.io.*;

?

What happens? Does the JVM import all the classes if using a wildcard?

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Stefan Ram - 17 Dec 2007 23:24 GMT

>more efficient than

There is run-time efficiency, memory efficiency, disk usage
efficiency ...

>What happens? Does the JVM import all the classes if using a wildcard?

An import declaration allows a static member or a named type
to be referred to by a simple name that consists of a single
identifier. I don't think that the JVM is aware of it at all.

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Arne Vajhøj - 18 Dec 2007 01:18 GMT

> An import declaration allows a static member or a named type
> to be referred to by a simple name that consists of a single
> identifier. I don't think that the JVM is aware of it at all.

I don't think he asked for static import just plain import.

Arne

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Lew - 18 Dec 2007 03:41 GMT

>> An import declaration allows a static member or a named type
>> to be referred to by a simple name that consists of a single
>> identifier. I don't think that the JVM is aware of it at all.
>
> I don't think he asked for static import just plain import.

The answer is the same for both domains of discourse - there is no run-time
impact.

Signature

Lew

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Arne Vajhøj - 18 Dec 2007 03:47 GMT

>>> An import declaration allows a static member or a named type
>>> to be referred to by a simple name that consists of a single
[quoted text clipped - 4 lines]
> The answer is the same for both domains of discourse - there is no
> run-time impact.

Yep.

But maybe the original poster were a bit confused by the explanation.

Arne

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Mark Rafn - 18 Dec 2007 00:12 GMT

>Is importing a class directly ie.

>import java.io.InputStream
>more efficient than
>import java.io.*;

It has no effect on the generated class, so no effect on runtime efficiency.
It's probabaly a hair faster to compile.

As a developer, I prefer specific imports, as it's easy to expand a classname
if the import is there, rather than having to search through a bunch of
packages to see where SomeFooAccessor is defined.

>What happens? Does the JVM import all the classes if using a wildcard?

No. The JVM doesn't see imports. They're thrown away by the compiler. The
compiler uses them to replace short type names with fully-qualified names.
There is no bytecode difference between importing specific names, wildcards,
and not importing anything in favor of using fully-qualified names everywhere.
--
Mark Rafn dagon@dagon.net <http://www.dagon.net/>

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Roedy Green - 18 Dec 2007 01:38 GMT

>Is importing a class directly ie.
>
[quoted text clipped - 3 lines]
>
>import java.io.*;

import is a purely a compile time feature. It has no effect on run
times. See http://mindprod.com/jgloss/import.html
on rules of thumb on how to use it.

Signature

Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com

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Crouchez - 18 Dec 2007 03:49 GMT

of course it's compile time isn't it, doh

cheers for the help

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Import efficiency

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