The Java interface to the dtSearch Engine is based on the Java Native Interface (JNI). Therefore, both the Java classes and a platform-specific binary executable are needed to use it. The Java classes are in examples\java\classes\dtSearchEngine.jar, which must be on the CLASSPATH. Adding the dtSearch Engine examples/java/classes folder to the CLASSPATH, or copying its contents to a folder on the CLASSPATH, will make these classes available in Java.
Under Linux, the binary executable is libdtsearch.so, which must be accessed through a symbolic link named libdtsjava.so. libdtsjava.so must be in a folder that is on the LD_LIBRARY_PATH, or you will get an "Unsatisfied Link" exception when you try to use the dtSearch Engine classes in Java. You can also copy the dtSearch .so files to your /usr/local/lib folder, or use ldconfig to make them accessible on your system.