1. When classpath is used, jar command is ignored . So use "classpath" with class file and "cp" with jar file   2. NEVER FORGET TO PUT : even you use only 1 external jar. In some cases you will get compilation error if you don't put :   java  -classpath  /media/Data/eclipseWorkspace/myExternalJar/commons-math-1.2.jar :   com.cbrc.motifmap.CombinationOfTF   java  -cp /media/Data/eclipseWorkspace/myExternalJar/commons-math-1.2.jar:    -jar myJar.jar