title: What is "compiler compliance level" in Eclipse?
body: <p>For some time I tried to understand, but I still don't get exactly what "compiler compliance level" for a project in Eclipse means. I looked all over this site and Google and couldn't find an answer I could understand.</p>
  
  <p>Let's say I want my program to be able to run on JRE 6.</p>
  
  <p>I can do: Project > Preferences > Java Build Path > Libraries, and set the JRE library I use to JRE 6.</p>
  
  <p>Why isn't this enough?</p>
  
  <p>I never understood why I also need to set the compiler compliance setting to JRE 6.</p>
  
  <p>I'd like to understand the difference between using JRE 6 in a project, and setting the project's compiler compliance setting to JRE 6.</p>
  
  <p><strong>What exactly does compiler compliance level mean?</strong></p>