recently I tried to do some modifications to the simulator in Eclipse on a system with Java 7. Additionally installing Java 6 solved this problem. It would be better, if the simulator worked with Java 7-only systems.
Java 6 is still the most widely used version of Java, therefore the default compile target is configured to Java 6. Nevertheless, you can configure your IDE to compile the code with an installed Version 7 of Java to compile with target Java version 6.