I agree with chrylis: you believe you changed your project’s compliance settings but probably you didnt.
Right click on your project and:
- Java / Build Path : Go to Libraries tab and ensure yourself that you are really using jre6
- Java / Compiler : Ensure yourself that you have selected 1.6 compliance
By the way you can “tell” eclipse that jre8 is 1.6 compliance clicking on Window/Preferences/Java/Installed JREs/Execution Environment and selecting in the left panel, Execution Environments, JavaSE-1.6 and in the Compatible JRE’s panel, jre8