Where is my Java SDK 7u7 installed?
I found Java 1.7 SDK in /Library/Java/JavaVirtualMachines/jdk1.7.0_07.jdk, and all the binaries in /Library/Java/JavaVirtualMachines/jdk1.7.0_07.jdk/Contents/Home/bin. 



And by clicking the jdk file, I could arrange the order so that Java SE 7 is executed first.

java -version
java version "1.7.0_07"
Java(TM) SE Runtime Environment (build 1.7.0_07-b10)
Java HotSpot(TM) 64-Bit Server VM (build 23.3-b01, mixed mode)


And I could also bring up the app from /Applications/Utilities/Java Preferences.app



For eclipse, I could add one line in /Applications/eclipse/Eclipse.app/Contents/MacOS/eclipse.ini to teach eclipse what Java it will use : 

-vm
/System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Home/bin/java