Now it is possible to install openjdk-11 this way:

sudo apt-get install openjdk-11-jdk

(Previously it installed openjdk-10, but not anymore)

1. You have to install the openjdk-8-jre:

    sudo apt-get install openjdk-8-jre
   

2. Next switch to the jre-8 version:

    $ sudo update-alternatives --config java
    There are 2 choices for the alternative java (providing /usr/bin/java).
   
    Selection    Path                                            Priority   Status
   
    * 0            /usr/lib/jvm/java-9-openjdk-amd64/bin/java       1500      auto mode
      1            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1500      manual mode
      2            /usr/lib/jvm/java-9-openjdk-amd64/bin/java       1500      manual mode
   

3. Add JAVA_HOME variable:

    export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
   

4. check java version:

    $ java -version
    openjdk version "1.8.0_151"
    OpenJDK Runtime Environment (build 1.8.0_151-8u151-b12-0ubuntu0.17.10.2-b12)
    OpenJDK 64-Bit Server VM (build 25.151-b12, mixed mode)
   

Same procedure for Oracle java.

Note: WebUpd8 team's PPA has been discontinued with effective from April 16, 2019. Thus this PPA doesn't have any Java files. More information can be found on PPA's page on Launchpad. Hence this method no longer works and exists because of historical reasons.

Use ppa :

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer

if you want java8 :

sudo apt-get install oracle-java8-installer

If you ABSOLUTELY need to have the latest update of java you must manualy install from official source, follow this tuto : http://www.cyberciti.biz/faq/howto-installing-oracle-java7-on-ubuntu-linux/

But I advise you to wait as ppa update

You can manipulate your own PATH. The usual suggestion is a JAVA_HOME environment variable. Add the lines to your .bashrc to keep through logout / reboot.

export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64
export PATH=$JAVA_HOME/bin:$PATH