Ant Javac任务删除方法

Question

I have run into some trully bizarre behavior in a Java project. The situation is that javac seems to be removing a method from a class during compilation.

The class looks something like this:

public class MessedUp extends X {
    //a bunch of variables here
    //a bunch of methods here

    public void thisDisappears(String arg){

    }

    //a bunch more methods here

}

There is another class that instantiates and calls this method:

public class WontCompile {

    public void doSomething(){
        MessedUp mu = new MessedUp();
        mu.thisDisappears("something");
    }
}

The first class compiles just fine, but the second doesn't. javac outputs something like the following:

[javac] C:\mypath\WontCompile.java:251: error: cannot find symbol
[javac]                     mu.thisDisappears("something");
[javac]                       ^
[javac]   symbol:   method thisDisappears(String)
[javac]   location: variable mu of type MessedUp

I know that the code is fine because I have been using it in Eclipse for a couple of years (I'm tracking down this problem as I try to use the ant file Eclipse produced). However, once in a while Eclipse will highlight the call to thisDisappears , saying it doesn't exist, and offering to create it. If accept the offer, then Eclipse complains that there are two methods with the same name. After a little bit of finagling which apparently causes a rebuild or something, the error goes away.

After being driven up the while for a while, I decided to check the actual class file for MessedUp.java. Using the Java Decompiler GUI , I found that thisDisappears isn't present in the class file!

Below is my ant file:

<project basedir="." default="build" name="MyProject">
    <property name="LIB_HOME" value="C:\dev\LibSuite-9.3.1"/>
    <property environment="env"/>
    <property name="debuglevel" value="source,lines,vars"/>
    <property name="target" value="1.7"/>
    <property name="source" value="1.7"/>
    <path id="MyProject.classpath">
        <pathelement location="bin"/>
        <pathelement location="lib/edu.mit.jwi_2.1.4.jar"/>
        <pathelement location="lib/edu.sussex.nlp.jws.beta.11.jar"/>
        <pathelement location="lib/jaws-bin.jar"/>
        <pathelement location="lib/junit-4.11.jar"/>
        <!--External Jars-->
        <pathelement location="${LIB_HOME}/share/java/abc.jar"/>
        <pathelement location="${LIB_HOME}/share/java/def-9.3.1.jar"/>
    </path>
    <target name="init">
        <mkdir dir="bin"/>
        <copy includeemptydirs="false" todir="bin">
            <fileset dir="main/src">
                <exclude name="**/*.launch"/>
                <exclude name="**/*.java"/>
            </fileset>
        </copy>
        <copy includeemptydirs="false" todir="bin">
            <fileset dir="main/test">
                <exclude name="**/*.launch"/>
                <exclude name="**/*.java"/>
            </fileset>
        </copy>
    </target>
    <target name="clean">
        <delete dir="bin"/>
    </target>

    <target depends="init" name="build">
        <echo message="${ant.project.name}: ${ant.file}"/>
        <javac debug="true" debuglevel="${debuglevel}" destdir="bin" includeantruntime="false" source="${source}" target="${target}">
            <classpath refid="MyProject.classpath"/>
            <src path="main/src"/>
            <src path="main/test"/>
            <compilerarg value="-Xlint"/>
        </javac>
    </target>

    <!--Test the app-->
    <target depends="build" name="regression">
        <junit>
            <classpath refid="MyProject.classpath"/>
            <test name="uni.my.app.TestSuite"/>
        </junit>
    </target>

    <!--Run the app-->
    <target depends="build" name="run">
        <java classname="uni.my.app.Application">
            <classpath refid="MyProject.classpath"/>
            <arg value="sentences.txt"/>
        </java>
    </target>
</project>

Unfortunately, I was unable to put together a minimum breaking example. The code I am working on is not yet released to the public, so I can't share it all yet. It references several jars (with no conflicting namespaces), some with native methods. I have no idea what exact combination of classes and jars causes the error. I had the same problem using jdk 1.6.0_25 and 1.7.21.

Does anyone have any experience or ideas on how to solve this problem?

Answer 1

This is a guess.

Ant operates outside of eclipse, and therefore any changes it makes are not reflected in eclipse's massively cached view of the world. For all I know, eclipse's changes are not reflected in files that ant uses, either.

I would do a project clean, then a project build, then a project refresh. I would see if you have this problem from within eclipse. Then I would run ant (if I must), do another refresh, and see if the problem exists then.

Any time you do anything in either eclipse or ant, before you use the other program, refresh the eclipse project.

Let us know how it goes.

ps trust that the java compiler is not removing any methods. I agree you have something strange going on, but that isn't it.

Answer 2

The problem was that, for whatever reason, another user had turned the project into the VCS with all of the class files in the same folders as their corresponding sources. On my machine, Eclipse puts the binaries into the bin folder, so I don't know why they were placed with the source on the other user's machine.

The init target generated by Eclipse is meant to copy over resources used by the code. It copies over anything but java or launch files from the source directories. However, since the class files were in the source directories, it copied them over, too. Then, when the build target was executed, it didn't bother compiling anything because it seemed that there were already fresh class files present (but they were actually just fresh copies of old code).

The solution was to 1) remove all of the class files from the source folders and 2) add exclude rules for **/*.class to the resource copying code, for good measure.