See these pages for more details on how to install Java:
https://help.ubuntu.com/community/Java
http://docs.oracle.com/javase/8/docs/technotes/guides/install/linux_jdk.html

Download the JDK/JRE: http://www.oracle.com/technetwork/java/javase/downloads/index.html

Extract the file "jdk-8u111-linux-x64.tar.gz" in the folder you want to install Java: /opt/jdk1.8.0_111
$ tar -xf jdk-8u111-linux-x64.tar.gz -C /opt/
Change the folder permissions:
$ chmod -R 755 /opt/jdk1.8.0_111 $ sudo chown -R mtitek /opt/jdk1.8.0_111 $ sudo chgrp -R mtitek /opt/jdk1.8.0_111
Setup the environment variables JAVA_HOME and PATH:

• Open the file ".profile": $ vi ~/.profile
  
• Append the following lines: export JAVA_HOME=/opt/jdk1.8.0_111 export PATH=$JAVA_HOME/bin:$PATH
  
• Reload the file ".profile": $ source ~/.profile
  
• Verify the environment variables: $ echo $JAVA_HOME $ echo $PATH
  

Locate the default java program file: $ which java /opt/jdk1.8.0_111/bin/java
Note that on macOS you might get an error similar to this one when you launch java commands:
"jdk-13.0.1.jdk cannot be opened because the developer cannot be verified ..."
To fix this issue run the following command on the jdk package before extracting it:
$ xattr -d com.apple.quarantine jdk-13.0.1_osx-x64_bin.tar

1. Check defaults
   Note that these folders may not exist yet in your computer!
   $ ls -al /usr/bin/java lrwxrwxrwx 1 root root /usr/bin/java -> /etc/alternatives/java
   $ ls -al /etc/alternatives/java lrwxrwxrwx 1 root root /etc/alternatives/java -> /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
   $ ls -al /usr/lib/jvm/default-java lrwxrwxrwx 1 root root /usr/lib/jvm/default-java -> java-1.7.0-openjdk-amd64
2. Add a new java alternative to the system
   sudo update-alternatives --install "/usr/bin/java" "java" "/opt/jdk1.8.0_66/bin/java" 1
   $ update-alternatives --display java java - auto mode link currently points to /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java /opt/jdk1.8.0_66/bin/java - priority 1 /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java - priority 1071 slave java.1.gz: /usr/lib/jvm/java-7-openjdk-amd64/jre/man/man1/java.1.gz Current 'best' version is '/usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java'.
3. Configure java alternatives
   $ 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-7-openjdk-amd64/jre/bin/java 1071 auto mode 1 /opt/jdk1.8.0_66/bin/java 1 manual mode 2 /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java 1071 manual mode Press <enter> to keep the current choice[*], or type selection number: 1 update-alternatives: using /opt/jdk1.8.0_66/bin/java to provide /usr/bin/java (java) in manual mode
4. Set JAVA_HOME
   export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")