Linux jdk

export JAVA_HOME=/usr/lib/jvm/java-7-sun  
export JRE_HOME=${JAVA_HOME}/jre  
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib  
export PATH=${JAVA_HOME}/bin:$PATH 

add path in /etc/profile

and setting defualt path and jdk version

    sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-7-sun/bin/java 300  
    sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/java-7-sun/bin/javac 300  

sudo update-alternatives --config java