code: private static Class<?> loadColtClass(String className) 
              throws ClassNotFoundException { 
          try {
              Class<?> clazz = 
                  Class.forName(className);
              return clazz;
              
          } catch (ClassNotFoundException cnfe) {
  
              // If we see a CNFE, don't immediately give up.  It's most likely
              // that this class is being invoked from inside a .jar, so see if
              // the user specified where COLT is manually.
              String coltProp = System.getProperty("colt.path");
              
              // if not, rethrow since the class does not exist
              if (coltProp == null)
                  throw cnfe;
  
              File coltJarFile = new File(coltProp);
              try {
                  // Otherwise, try to load the class from the specified .jar
                  // file.  If the ClassLoader for loading all COLT classes has
                  // not yet been initialized, do so now.  We need to maintain
                  // only one class loader for all COLT classes, otherwise the
                  // reflective invocation will fail; the constructor type system
                  // does not work correctly if the parameter objects have been
                  // loaded from a different class loader. --jurgens
                  if (coltClassLoader == null) {
                      coltClassLoader = 
                          new java.net.URLClassLoader(
                          new java.net.URL[] { coltJarFile.toURI().toURL() });
                  }
  
                  Class<?> clazz = Class.forName(className, true,
                                                 coltClassLoader);
                  return clazz;
              } catch (Exception e) {
                  // fall through and rethrow original
              }
              
              throw cnfe;
          }
      }
docs: Reflectively loads the COLT-related class.  If the class is not
  immediately loadable from the existing classpath, then this method will
  attempt to use the {@code colt.path} system environment variable to load
  it from an external resource.