是否有可能为同一javac编译器来编译同一套源文件而产生不同的校验的类文件？ [英] Is it possible for the same javac compiler to compile the same set of source files but produce class files of different checksums?
问题描述
我试图来比较这个结果：（蚂蚁）
＆LT; javac的
目标=1.5
来源=1.5
德precation =上
叉=YES
优化=真
调试=真
DEBUGLEVEL =行，增值经销商，源＆GT; ＆LT;＆类路径GT;
＆LT;文件集DIR =$ {} project.basedir LIB /../＆GT;
＆LT;包括姓名=** / *罐子。/＆GT;
＆LT;包括姓名=** / *拉链。/＆GT;
＆LT; /文件集＆GT;
＆LT; /类路径＆GT;
＆LT; / javac的＆GT;
...反对这种（在Maven中）
＆LT;＆插件GT;
＆LT;＆的artifactId GT; Maven的编译器插件＆LT; / artifactId的＆GT;
＆LT;＆版GT; 2.3.2＆LT; /版本＆GT;
＆LT;＆执行GT;
＆LT;执行与GT;
＆LT;＆ID GT;＆编译LT; / ID＆GT;
＆LT;阶段＆gt;＆编译LT; /阶段＆gt;
＆LT;目标＆GT;
＆LT;＆目标GT;＆编译LT; /目标＆GT;
＆LT; /目标＆GT;
＆LT;结构＆gt;
＆lt;目标＆GT; 1.5 LT; /目标与GT;
＆lt;信源＆GT; 1.5 LT; /源＆GT;
＆LT;调试和GT;真＆LT; /调试＆GT;
＆LT;＆DEBUGLEVEL GT;线，增值经销商，源＆LT; / DEBUGLEVEL＆GT;
＆LT; showDe precation＆GT;真＆LT; / showDe precation＆GT;
＆LT;优化＆GT;真＆LT; /优化＆GT;
＆LT;＆叉GT;真＆LT; /前叉＆GT;
＆所述包括（includes）GT;
...
＆LT; / - 包括GT;
＆LT; /结构＆gt;
＆LT; /执行＆GT;
＆LT; /处决＆GT;
＆LT; /插件＆GT;
...才发现，所产生的类文件2具有略微不同的校验和，而其余的都是相同的。我认为多线程已经发挥了作用，但对于任一选项产生的校验似乎是在重复尝试是一致的。什么都不可能解释这一结果呢？
更新：
我已经检查一组使用不同的校验文件的的javap -verbose ，发现唯一的区别是：
常量＃16 =＃类108; //爪哇/郎/异常
常量＃17 =方法＃102＃109; //的Java / IO / Writer.close :(）V
常量＃18 =方法＃7＃109; //的Java / IO / FileWriter.close :(）V
，而不是
常量＃16 =方法＃102＃108; //的Java / IO / Writer.close :(）V
常量＃17 =方法＃7＃108; //的Java / IO / FileWriter.close :(）V
常量＃18 =＃类109; //爪哇/郎/异常
为您呈现，不同的是在生成的常量池，这实在是一个不是问题的问题，但是麻烦你所期望的一样相同的输出编译器和选项。我敢打赌，编译器调用在两种情况之间不同的顺序java文件和编译的顺序影响结果。
I was attempting to compare the results of this: (in ant)
<javac
target="1.5"
source="1.5"
deprecation="on"
fork="yes"
optimize="true"
debug="true"
debuglevel="lines,vars,source">
<classpath>
<fileset dir="${project.basedir}/../lib">
<include name="**/*.jar" />
<include name="**/*.zip" />
</fileset>
</classpath>
</javac>
...against this: (in maven)
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<executions>
<execution>
<id>compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<target>1.5</target>
<source>1.5</source>
<debug>true</debug>
<debuglevel>lines,vars,source</debuglevel>
<showDeprecation>true</showDeprecation>
<optimize>true</optimize>
<fork>true</fork>
<includes>
...
</includes>
</configuration>
</execution>
</executions>
</plugin>
...only to discover that 2 of the resulting class files have slightly different checksums, while the rest are identical. I consider multi-threading to have played a part, but the checksums produced for either option appear to be consistent upon repeated attempts. What can possibly account for this result?
Update:
I have examined one set of the files with different checksums using javap -verbose and noticed the only difference being:
const #16 = class #108; // java/lang/Exception
const #17 = Method #102.#109; // java/io/Writer.close:()V
const #18 = Method #7.#109; // java/io/FileWriter.close:()V
as opposed to:
const #16 = Method #102.#108; // java/io/Writer.close:()V
const #17 = Method #7.#108; // java/io/FileWriter.close:()V
const #18 = class #109; // java/lang/Exception
as you showed, the difference is in the generated constant pool, which is really a non-issue, but troubling as you would expect the same output with the same compiler and options. i would bet that the compiler is called with the java files in different order between the two situations, and the order of compilation is affecting the result.
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