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<title>Classpath and Sourcepath</title>
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<h2>Classpath and Sourcepath</h2>
<h3>Class Path</h3>
<p>The classpath in JSwat is used much the same way the Java
Virtual Machine uses it. The classpath provides a list of locations
where classes can be found on the system. The entries correspond to
directories containing the classes concerned. For example, on my
system the classpath is set to <code>/home/nfiedler/java</code> and
all of my Java code resides inside that directory or subdirectories
therein.</p>
<p>The way in which JSwat handles the classpath is quite simple.
When the session is inactive, the classpath is simply that which
was set via the <code>classpath</code> command or the "Set
Classpath" dialog. If no setting is available, then JSwat
takes the classpath from the
"<code>java.class.path</code>" property, or if that
property is not defined, the current working directory is used.
When JSwat launches a new debuggee VM it sets the classpath of the
debuggee VM to that which is set in JSwat. When JSwat is connecting
to a remote debuggee VM then the classpath in JSwat becomes the
classpath of the remote VM. Thus you will probably see a different
classpath value depending on whether a remote debugging session is
active or not.</p>
<p>When using either the <code>load</code> command or the
"Start VM" dialog, you may provide an alternate value for
the classpath. You do this with the "<code>-cp</code>" or
"<code>-classpath</code>" Java VM options, just as you
would when invoking '<code>java</code>' from the command
line. This will override (and overwrite) the classpath value
defined in JSwat.</p>
<p>See the help for the <code>classpath</code> JSwat command to
learn how to view and set the classpath used by JSwat. An easier
way to modify the classpath is through the "Set
Classpath" menu item in the "Options" menu.</p>
<h3>Source Path</h3>
<p>The sourcepath in JSwat looks just like a classpath setting.
However, it is used only for finding source files. The sourcepath
is used by JSwat as another means of finding the source file for a
class. If a sourcepath is not set, JSwat will fall back on the
classpath to find the source files.</p>
<p>The format of the sourcepath is exactly like the classpath. That
is, if your source code is in <code>/usr/source/stuff</code> and
your classes are in <code>/usr/classes/stuff</code> and the name of
your class is <code>stuff.Test</code>, then the sourcepath should
be set to <code>/usr/source</code>, just as the classpath is set to
<code>/usr/classes</code>. You may also add Zip or Jar files to
your sourcepath, and JSwat will find the source files inside of the
named archives. Just as with the directories, the paths of the
files in the archives must match the fully-qualified names of the
classes (e.g. "<code>java/lang/String.java</code>" for
"<code>java.lang.String</code>").</p>
<p>The sourcepath can be set one of two ways in JSwat. First, it
can be passed when launching JSwat using the <code>-D</code>
argument to the JVM, like so:</p>
<pre>
% java -Djava.source.path=/usr/java/src com.bluemarsh.jswat.Main
</pre>
<p>This value will override any previous sourcepath setting in
JSwat. This is unlike the classpath, which defaults to the setting
in JSwat rather than the <code>java.class.path</code> property
setting.</p>
<p>The second way to set the sourcepath is with the
<code>sourcepath</code> JSwat command. This works just like the
<code>classpath</code> command and takes a set of directory paths
and or Zip/Jar files as an argument. On Windows the directory paths
are separated with '<code>;</code>' characters, while on
Unix systems it is the '<code>:</code>' character. An
easier way to modify the sourcepath is through the "Set
Sourcepath" menu item in the "Options" menu.</p>
<h3>How JSwat Finds Source Files</h3>
<p>Apparently this is complicated because new users run into this
problem with surprising frequency. It generally boils down to a
misunderstanding of how the classpath and sourcepath are used. Keep
in mind that JSwat uses the classpath pretty much the way you would
expect. It is generally where Java source files (and class files)
are found. The sourcepath is a set of alternative paths for finding
source files, taking precedence over the classpath.</p>
<p>Let's look at a detailed example. Take for instance the
class "<code>java.lang.String</code>". Let's assume
the source file is called <code>String.java</code> and is located
in <code>/usr/java/src/java/lang</code>. If the classpath is set to
something like <code>/usr/java/jre/lib/rt.jar</code> then JSwat is
not going to be able to find the source for
<code>java.lang.String</code> since it has no idea where on the
file system the file could be located.</p>
<p>This is where the sourcepath comes in. With the classpath set to
<code>/usr/java/jre/lib/rt.jar</code>, JSwat only sees class files
in that jar file. If we set the sourcepath to be
<code>/usr/java/src</code> then JSwat will look for the file named
<code>/usr/java/src/java/lang/String.java</code>. Lo and behold,
there is the source code.</p>
<p>If this still does not make sense, read this page again until it
does. I have explained this as simply as I can and provided
multiple examples. If you cannot figure it out, you probably are
confused with the classpath and should read a book on Java until
you have grasped the concept.</p>
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