#!/bin/bash

if [ -z "$1" ]
  then
    echo "usage:"
    echo $0 path/to/jdk-or-jre.tar.gz
    echo 
    echo "the parmeter is the (absolute or relavive) path to the file you downloaded from Oracle website."
else   
  isJdk=$(echo $1 | grep 'jdk' -m 1 -o )
  if [ "$isJdk"  =  'jdk' ]
  then
    alternatives_files="java javaws javac jar"
  else  
    alternatives_files="java javaws"
  fi
  echo extract $1 to /opt/Oracle_Java ...
  sudo mkdir -p  /opt/Oracle_Java
  sudo  tar -xzf $1 -C  /opt/Oracle_Java
  new_version=/opt/Oracle_Java/$(tar -tzf $1 | grep '^[^/]*' -m 1 -o)
  echo setting alternatives to new version $new_version  ...
  for f in $alternatives_files
  do
    sudo update-alternatives --install "/usr/bin/$f" "$f" "$new_version/bin/$f" 1
    sudo update-alternatives --set "$f" "$new_version/bin/$f"
  done
fi