linux 配置java环境变量，并即时生效

JAVA_HOME=/usr/local/jdk1.6.0_37
JRE_HOME=/usr/local/jdk1.6.0_37/jre
CLASSPATH=$JAVA_HOME/lib:$JAVA_HOME/jre/lib
PATH=$JAVA_HOME/bin:$PATH
export PATH CLASSPATH JAVA_HOME

------------------------------------------

JAVA_HOME=/usr/java/jdk1.8.0_101
CLASSPATH=$JAVA_HOME/lib/
PATH=$PATH:$JAVA_HOME/bin
export PATH JAVA_HOME CLASSPATH

-------------------------------------------

export PATH=$PATH:/usr/local/python27/bin