java.lang.UnsupportedClassVersionError in eclipse [duplicate]

Question

I am not a Java programmer really, so I am posting this question. The exception is being thrown java.lang.UnsupportedClassVersionError in my main class in an eclipse project. If I comment out the imports that this class has, it compiles and runs fine. If I put the imports back in, it does not work. Does this mean that the libraries I am importing were compiled with a newer or older version of java than I have? when i do java -version on the system i get 1.5_07

I could've sworn this was actually working last week, but maybe some setting in eclipse got tweaked? Is the Java Build Path in eclipse what I need to look for to check the JRE and compiler versions?

Answer 1

In Eclipse, the compiler version is set independent of the JRE version. That means you can set the compiler to Java version 1.6 and use the JRE 1.5. In this case, you compiled classes cannot be run.

You can check the preferences in Window / Preferences / Java / Compiler for the default compiler compliance level, or the properties of your project for a project specific compiler compliance level. Compare that level with the JRE used in your project (Project / Properties / Java Build Path -> Libraries / JRE System Library) and in your program's launch configuration (via the Run / Run Configurations... menu).