How to check Oracle java development tool is installed on my Ubuntu

Sometimes I want to know what kind of java am I use and how to check it.
In this case, "java -version" command is not helpful.

$ java -version
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)

Using this command, I don't know what kind of JDK am I use between openjdk or OracleJDK.

To know it, "update-java-alternatives -l" command is used.

$ update-java-alternatives -l
java-8-oracle 1 /usr/lib/jvm/java-8-oracle

In my case, there is only one JDK on my Ubuntu. If you have several versions and kinds of JDK, you should check which one you are using.

$ which javac
/usr/bin/javac
$ ls -al /usr/bin/javac
... /usr/bin/javac -> /etc/alternatives/javac
$ ls -al /etc/alternatives/javac
... /etc/alternatives/javac -> /usr/lib/jvm/java-8-oracle/bin/javac

#OracleJDK, #SUNJDK, #openjdk