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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
Newsgroups: comp.lang.java.programmer
Subject: Re: about class dependancies
Date: Wed, 2 Dec 2015 21:58:08 -0500
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On 12/2/2015 9:55 PM, Arne Vajhøj wrote:
> On 12/2/2015 8:26 PM, regis wrote:
>> On 12/03/15 02:05, Stefan Ram wrote:
>>> regis <regis.barbanchon@free.fr> writes:
>>>> It still seems to work if it is made final...
>>>
>>> echo >A.java public final class A { public static void main( final
>>> java.lang.String[] args ){ java.lang.System.out.println( B.x ); }}
>>> echo >B.java public final class B { public static final int x = 1; }
>>> javac A.java
>>> javac B.java
>>> java A
>>> RENAME A.class hide.class
>>> echo >B.java public final class B { public static final int x = 2; }
>>> javac B.java
>>> DELETE A.class
>>> RENAME hide.class A.class
>>> java A
>>>
>>>    Now it still prints 1, not 2.
>>>
>>>    The above script assume Microsoft® Windows.
>>>    You might have to adjust it for your environment.
>>
>> Ah, interesting...
>> so a non-updated file A.class can indeed be tricked by a change in B...
>
> What is happening is seen with this:
>
> public class B {
>      public static final int K = 123;
> }
>
> public class A {
>      public static void main(String[] args) {
>          System.out.println(B.K);
>          System.out.println(123);
>      }
> }
>
> C:\Work>javap -c A
> Compiled from "A.java"
> public class A {
>    public A();
>      Code:
>         0: aload_0
>         1: invokespecial #1                  // Method
> java/lang/Object."init>":()V
>         4: return
>
>    public static void main(java.lang.String[]);
>      Code:
>         0: getstatic     #2                  // Field
> java/lang/System.out:Ljava/io/PrintStream;
>         3: bipush        123
>         5: invokevirtual #4                  // Method
> java/io/PrintStream.println:(I)V
>         8: getstatic     #2                  // Field
> java/lang/System.out:Ljava/io/PrintStream;
>        11: bipush        123
>        13: invokevirtual #4                  // Method
> java/io/PrintStream.println:(I)V
>        16: return
> }
>
> A.class does not contain a named reference to B.K instead
> A.class contains the while of B.K from the time of compilation.

Note that the practical impact of this is close to zero.

Practically everyone starts a Java build by deleting all the
previously build class files.

Arne