Enhance the build file
Now we have a working buildfile we could do some enhancements: many time you are referencing the same directories, main-class and jar-name are hard coded, and while invocation you have to remember the right order of build steps.
The first and second point would be addressed with properties, the third with a special property - an attribute of the <project>-tag and the fourth problem can be solved using dependencies.
<project name="HelloWorld" basedir="." default="main">
<property name="src.dir" value="src"/>
<property name="build.dir" value="build"/>
<property name="classes.dir" value="build/classes"/>
<property name="jar.dir" value="build/jar"/>
<property name="main-class" value="oata.HelloWorld"/>
<target name="clean">
<delete dir="build"/>
</target>
<target name="compile">
<mkdir dir="${classes.dir}"/>
<javac srcdir="src" destdir="${classes.dir}"/>
</target>
<target name="jar" depends="compile">
<mkdir dir="${jar.dir}"/>
<jar destfile="${jar.dir}/apache-ant.jar" basedir="${classes.dir}">
<manifest>
<attribute name="Main-Class" value="${main-class}"/>
</manifest>
</jar>
</target>
<target name="run" depends="jar">
<java jar="${jar.dir}/apache-ant.jar" fork="true"/>
</target>
<target name="clean-build" depends="clean,jar"/>
<target name="main" depends="clean,run"/>
</project>
Now it's easier, just do a ant and you will get
Buildfile: build.xml clean: compile: [mkdir] Created dir: C:\...\build\classes [javac] Compiling 1 source file to C:\...\build\classes jar: [mkdir] Created dir: C:\...\build\jar [jar] Building jar: C:\...\build\jar\HelloWorld.jar run: [java] Hello World main: BUILD SUCCESSFUL
