build.xml

<project name="myproject" default="dist" basedir=".">
	<property name="src.dir" value="src" />
	<property name="build.dir" value="build" />
	<property name="dist.dir" value="dist" />
	<path id="project.classpath">
		<pathelement location="${build.dir}"/>
	</path>

	<target name="compile" description="Compile the project">
		<mkdir dir="${build.dir}" />
		<javac destdir="${build.dir}" srcdir="${src.dir}" debug="true">
			<classpath refid="project.classpath"/>
		</javac>
	</target>
	
	<target name="dist" depends="compile" description="Make a JAR file for the project">
		<mkdir dir="${dist.dir}"/>
		<jar destfile="${dist.dir}/myproject.jar">
			<fileset dir="${build.dir}"/>
		</jar>
	</target>
	
	<target name="clean">
		<delete dir="${build.dir}"/>
		<delete dir="${dist.dir}"/>
	</target>
</project>