apt-get install jar

$ java -version
java version "1.8.0_40"
Java(TM) SE Runtime Environment (build 1.8.0_40-b25)
Java HotSpot(TM) Client VM (build 25.40-b25, mixed mode)

$ javac -version
javac 1.8.0_40

$ find / -type f -name "jar"

export PATH="$PATH:/usr/lib/jvm/java-7-openjdk-amd64/bin"

$ sudo ln -s /usr/lib/jvm/java-7-openjdk-amd64/bin/jar /usr/bin/jar

sudo apt-get install openjdk-7-jre # to be able to run
sudo apt-get install openjdk-7-jdk # to be able to compile

sudo add-apt-repository ppa:webupd8team/java -y
sudo apt-get update
sudo apt-get install oracle-java8-installer