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What counts as a reference?

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  What counts as a reference? Roedy Green <see_website@mindprod.com.invalid> - 2014-09-11 21:30 -0700
    Re: What counts as a reference? "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2014-09-12 11:19 +0100
    Re: What counts as a reference? Steven Simpson <ss@domain.invalid> - 2014-09-12 15:47 +0100
    Re: What counts as a reference? Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2014-09-12 21:53 -0700

#29947 — What counts as a reference?

I a suspicion that Java/genjar/Jet includes classes it does not really
need to.
I have not done full experiments.

I suspect an @see counts as a reference
I suspect that private static X x; counts as a reference even if there
is no mention of X or x elsewhere.

I wonder if anyone has ever dug into this or has read something on the
topic.
-- 
Roedy Green Canadian Mind Products http://mindprod.com
There are only two industries that refer to their customers as users.
~ Edward Tufte (born: 1942 age: 72)

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#29948

Roedy Green wrote:

> I suspect that private static X x; counts as a reference even if there
> is no mention of X or x elsewhere.

From memory of the JVM spec (not the Java spec), the reference "private static 
X x;" must cause the containing class to fail to load (I forget at what stage) 
if there is no class X.

It's a long time since the JVM spec was part of my daily reading, though.

    -- chris 

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#29949

On 12/09/14 05:30, Roedy Green wrote:
> I suspect an @see counts as a reference
> I suspect that private static X x; counts as a reference even if there
> is no mention of X or x elsewhere.

Use javap to check:

$ cat IsARef.java
/**
  * This class is pointless.
  *
  * @see Referenced
  */
public class IsARef {
     private static Runnable x;

     private static Class<?> y = Iterable.class;
}
$ cat Referenced.java
public class Referenced { }
$ javac IsARef.java
$ javap -verbose IsARef
[...]
Constant pool:
    #1 = Methodref          #5.#19         // java/lang/Object."<init>":()V
    #2 = Class              #20            // java/lang/Iterable
    #3 = Fieldref           #4.#21         // IsARef.y:Ljava/lang/Class;
    #4 = Class              #22            // IsARef
    #5 = Class              #23            // java/lang/Object
    #6 = Utf8               x
    #7 = Utf8               Ljava/lang/Runnable;
    #8 = Utf8               y
    #9 = Utf8               Ljava/lang/Class;
   #10 = Utf8               Signature
   #11 = Utf8               Ljava/lang/Class<*>;
   #12 = Utf8               <init>
   #13 = Utf8               ()V
   #14 = Utf8               Code
   #15 = Utf8               LineNumberTable
   #16 = Utf8               <clinit>
   #17 = Utf8               SourceFile
   #18 = Utf8               IsARef.java
   #19 = NameAndType        #12:#13        // "<init>":()V
   #20 = Utf8               java/lang/Iterable
   #21 = NameAndType        #8:#9          // y:Ljava/lang/Class;
   #22 = Utf8               IsARef
   #23 = Utf8               java/lang/Object
[...]

My understanding is that the only classes needed at runtime are those 
listed in the constant pool under "Class" (right?), of which there are 
only three above.  One of them is to the defined class itself, one is a 
reference to the base class, and the other is for the class literal for 
Iterable.  The @see has had no effect.  Names of Runnable and Class (the 
types of the two static fields) only exist in member signatures.

-- 
ss at comp dot lancs dot ac dot uk

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#29963

In article <mgt41aluh04qirbq20lrin09lbanr01shs@4ax.com>,
 Roedy Green <see_website@mindprod.com.invalid> wrote:

> I a suspicion that Java/genjar/Jet includes classes it does not really
> need to.
> I have not done full experiments.
> 
> I suspect an @see counts as a reference
> I suspect that private static X x; counts as a reference even if there
> is no mention of X or x elsewhere.
> 
> I wonder if anyone has ever dug into this or has read something on the
> topic.

@see, the JavaDoc annotation, has no influence on source code 
compilation.  Only a JavaDoc compiler uses it.

java.lang.annotation.Annotation (the @interface declarations) with 
RetentionPolicy of RUNTIME are loaded on demand for each class from 
bytecode then held in the java.lang.Class instance.

Unused static fields hold a reference to a class unless the source code 
compiler has been explicitly configured to remove them.  The reference 
begins when the class is initialized for use.

Referencing a class does not initialize the class; only using the class 
initializes it.  Therefore, a class referenced only by an unused static 
field may be loaded but not initialized.  A class that is loaded but not 
initialized will not load any other classes.  Loading old Apache 
spaghetti without this trick would be pretty much impossible.

-- 
I will not see posts from astraweb, theremailer, dizum, or google
because they host Usenet flooders.

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