First of all, download from the website of java.
I download 'jdk-8u102-linux-i586.tar.gz'
unzip it to the specifical derictory.
with the command:tar -zxvf jdk-8u102-linux-i586.tar.gz -C /home/sonn/Workspace/softwares/sonn_java/
then you just need to set the sys Path.with the commands:
sudo gedit /etc/environment
and the command 'source /etc/environment' to make it effective.
sudo gedit /etc/profile:
finally reboot the PC. and you can see if it have become effective.
then you can install eclipse, download and unzip.and go to the directory run command the file 'eclipse' to startup.
but..........................................................
that's really disgusting problem.
At last I found it was because I installed the jdk which was for 32-bit linux.
reinstall jdk with the right edition.
O.K.
THEN I CAN DEVELOP JAVA ON MY UBUNTU.
ENJOY IT.