how to configure jdk (eclipse luna)

Window > Preferences > Java > Installed JREs > Standart VM > JRE home

choose
C:\Program Files (x86)\Java\jdk1.8.0_31

C:\Users\jupiter>java -version
java version "1.8.0_31"
Java(TM) SE Runtime Environment (build 1.8.0_31-b13)
Java HotSpot(TM) Client VM (build 25.31-b07, mixed mode)