El Capitan

You will need Apple JDK 1.6 to run the JDeveloper installer. Download and install Apple Java 1.6 from: http://support.apple.com/kb/DL1572
After Apple JDK 1.6 was installed, you should check "Known Issues" from Jdev Release Notes and create symbolic link as mentioned above:

cd /Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/  
su root  
mkdir jre  
cd jre  
mkdir lib  
cd lib  
ln -s ../../../Classes/classes.jar rt.jar

And now you could run Jdev installer:

/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/bin/java -jar ~/Downloads/jdevstudio11119install.jar

When installer asks for JDK, point it to Oracle JDK 1.7 location. JDeveloper and integrated WebLogic Server will use Oracle JDK 1.7 after installation. You could find JDK 1.7 in your OS if you'll run:

/usr/libexec/java_home -v 1.7

Now get back to release notes and open jdev.conf from MW_HOME/jdeveloper/jdev/bin. Add this line to jdev.conf:

AddVmOption -Djava.io.tmpdir=/var/tmp

Now you can run Jdev!