build.xml

<project name="classloader-example">

    <target name="clean">
        <delete dir="bin"/>
        <delete dir="dynamic_classes_1"/>
        <delete dir="dynamic_classes_2"/>
    </target>

    <target name="compile">
        <mkdir dir="bin"/>
        <javac srcdir="src" destdir="bin"/>
        <mkdir dir="dynamic_classes_1"/>
        <javac srcdir="src_dynamic_1" destdir="dynamic_classes_1">
            <classpath>
                <pathelement location="bin/"/>
            </classpath>
        </javac>
        <mkdir dir="dynamic_classes_2"/>
        <javac srcdir="src_dynamic_2" destdir="dynamic_classes_2">
            <classpath>
                <pathelement location="bin/"/>
            </classpath>
        </javac>
    </target>

    <target name="run" depends="compile">
        <java classname="com.romanenco.cloader.Example">
            <classpath>
                <pathelement location="./bin"/>
         </classpath>
        </java>
    </target>

</project>