1 After downloading oracle jdk, extract it to the directory, such as: /home/tomsky/ide/jdk_1.8
2 sudo update-alternatives --install /usr/bin/java java /home/tomsky/ide/jdk_1.8/bin/java 300
sudo update-alternatives --install /usr/bin/javac javac /home/tomsky/ide/jdk_1.8/bin/javac 300
sudo update-alternatives --install /usr/bin/javap javap /home/tomsky/ide/jdk_1.8/bin/javap 300
sudo update-alternatives --install /usr/bin/javadoc javadoc /home/tomsky/ide/jdk_1.8/bin/javadoc 300
3 Switch java version when using
sudo update-alternatives --config java