I think the problem is with your classpath
path declaration. The build
directory should be a <pathelement>
<path id="classpath">
<fileset dir="${lib}">
<include name="**/*.jar" />
</fileset>
<pathelement location="${build}" />
</path>
Also, I would only include 3-rd party jars in your classpath
refid. So the whole block looks like.
<path id="3rd-party-classpath">
<fileset dir="${lib}">
<include name="**/*.jar" />
</fileset>
</path>
<target name="build">
<javac srcdir="${src}" destdir="${build}">
<classpath refid="3rd-party-classpath" />
</javac>
</target>
<target name="run">
<java classname="FirstClass">
<classpath>
<pathelement location="${build}" />
<path refid="3rd-party-classpath" />
</classpath>
</java>
</target>
Also, as DroidIn.net has pointed out, you should create a package for you program.