Open up terminal and check what java version is currently set in your path variable.
You can do that by typing in your terminal
java -version // this will check your jre version.
javac -version // this will check your compiler version
If this shows incorrect java version but you have installed java 1.8 then you have to set path variable to the newer version of java.
To do that do add the line:
export JAVA_HOME=/path/to/java/jdk1.x
to ~/.bash_profile (same as /Users/username/.bash_profile)
Then do this from the terminal to set the new variable
source ~/.bash_profile
Also what's your eclipse.ini set to ?
-Dosgi.requiredJavaVersion=1.7
EDIT:
Please open up terminal and type
find / -name "java" // This should find all folder named java on your file system.
Also how did you install java in the first place ?