Difference between setting classpath in build.xml using fileset and pathelement

Question

I have a build file that declares the classpath as shown

<path id="compile.classpath">
    <fileset dir="${basedir}/lib"    includes="**"/>        
    <fileset dir="${jboss.home}/lib" includes="**"/>        
    <pathelement path ="${build.classes.dir}"/>
</path>

I tried looking at the documentation but I am not able to understand the use of pathelement .

I know that the ID is used to refer to this class path while performing a task and fileset includes the jarfiles.

edit 1: My doubt is Why can't we use fileset to include the class files in place of pathelement ?

Answer 1

Latest edit:

My doubt is Why can't we use fileset to include the class files in place of pathelement?

If you use a fileset then you'd be adding a set of class files to the path as follows:

CLASSPATH=classes/MyClass1.class:classes/MyClass2.class:classes/MyClass3.class:....

When what Java expects to see is simply:

CLASSPATH=classes

Only jar (and WAR,EAR,etc) files are explicitly listed on the classpath (Java will open them up and load their class files), hence the need for a fileset in ANT.

Update

Here's the Oracle documentation:

• http://docs.oracle.com/javase/7/docs/technotes/tools/windows/classpath.html

Class paths to the .jar, .zip or .class files. Each classpath should end with a filename or directory depending on what you are setting the class path to:

• For a .jar or .zip file that contains .class files, the class path ends with the name of the .zip or .jar file.
• For .class files in an unnamed package, the class path ends with the directory that contains the .class files.
• For .class files in a named package, the class path ends with the directory that contains the "root" package (the first package in the full package name).

Answer 2

There was already similar question about 'pathelements' here . From the provided documentation: "If it's path structure like in your example: "A path-like structure can include a reference to another path-like structure (a path being itself a resource collection) via nested elements"

 <path id="base.path">
  <pathelement path="${classpath}"/>
  <fileset dir="lib">
    <include name="**/*.jar"/>
  </fileset>
  <pathelement location="classes"/>
</path>

If it's classpath structure: "The path attribute is intended to be used with predefined paths"

<classpath>
  <pathelement path="${classpath}"/>
  <pathelement location="lib/helper.jar"/>
</classpath>