openjdk 1.7 in eclipse: operator is not allowed for source level below 1.7
Solution 1:
In your project's preferences, you must set the compiler --source option to 1.7 and --target option to 1.7 also. There are dedicated option boxes for that.
Right-click on the project. Choose Properties. Choose Java Compiler on the left. Choose 1.7 for the Compiler Compliance level. If the 2 drop-downs below that aren't 1.7, uncheck Use default compliance settings and set those to 1.7.
Solution 2:
right click on the error, choose quick fix, and select change JRE to 1.7