Java path classpath and -D

1. 环境变量 $PATH - 系统寻找可执行文件目录：setenv PATH /usr1/arbor/3pjava/jdk/bin:$PATH. Once put the dir in $PATH then can excecute it directly in command line.

appletviewer  java            javapackager  jdb    jmc         jstat         pack200      serialver   xjc
ControlPanel  javac           java-rmi.cgi  jdeps  jmc.ini     jstatd        policytool   servertool
extcheck      javadoc         javaws        jhat   jps         jvisualvm     rmic         tnameserv
idlj          javafxpackager  jcmd          jinfo  jrunscript  keytool       rmid         unpack200
jar           javah           jconsole      jjs    jsadebugd   native2ascii  rmiregistry  wsgen
jarsigner     javap           jcontrol      jmap   jstack      orbd          schemagen    wsimport

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>java -version
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)

2. "CLASSPATH" class run depends jar package  like xxx.jar 1.jar 2.jar

3. "-D" depends not java jar or configuration file dir like -Djava.library.path=./libs, and other system parameter like -Dos.type=UNIX