han@ubuntu:/etc$ whereis java

java: /usr/bin/java /usr/share/java /usr/lib/jvm/java-8-openjdk-amd64/bin/java /usr/share/man/man1/java.1.gz

han@ubuntu:/etc$ ls -lrt /usr/bin/java

lrwxrwxrwx 1 root root 22 4月   2 15:54 /usr/bin/java -> /etc/alternatives/java

han@ubuntu:/etc$ ls -lrt /etc/alternatives/java

lrwxrwxrwx 1 root root 46 4月   2 15:54 /etc/alternatives/java -> /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java

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

export PATH=$JAVA_HOME/bin:$PATH

export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar

source /etc/profile

han@ubuntu:/etc$ echo $JAVA_HOME

/usr/lib/jvm/java-8-openjdk-amd64