Eclipse auto save before run

Here has the correct answer:

http://stackoverflow.com/questions/2943122/eclipse-auto-save

The second one is correct:

if 

Window -> Preferences -> General -> Workspace and there you can check "Save automatically before build" + "Build automatically" 

don't work try this 

Preferences -> Run/Debug -> Launching -> "Save dirty editors before launching"

Can't change default jre even though path has been modified

Problem:

The Path in environment variable is using JDK1.6 but java -version shows actually JRE 1.7 is being used.

Solution:

I am on a Windows 7 machine. I am using this way but I don't like it.

Go to C:\Windows\System32, change the java.exe and javaw.exe to whatever you like.
Then the system will pick up the setting in Path.

Unsupported major.minor version 49.0

The application is compiled by java 1.5, but I want to run it on a java 1.4 machine.