After I installed Eclipse, where can I specify a jdk version it's going to use ? will it use what I set up in the PATH for my PC (control panel-->System-->Environment variable-->PATH) automatically ? or will it use some jdk that may comes with eclipse software ?
In other words, if I want to use a different jdk version, shall I just change the PATh in my PC's environemnt variable, or shall I change some setting in Eclipse IDE ?
Go to "Java / Installed JREs" in the preferences. There you can point Eclipse to different JDKs/JREs and tell it which to use per default. You can also configure single projects and launch configurations to use others than the default.
Remember that you might also need to change the compiler compliance setting.
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus