Time to time you have a java project, which uses an old version of the JRE compiler. Installing old java versions on OS X is quite tricky and not necessary. You can use the compiler compliance level feature in Eclipse IDE. This setting just tells the compiler to pretend it’s a different version of Java.
To change the compiler compliance level, go to your
Project Settings -> Java Compiler.
Use compliance from execution environment and ensure that
Use default compliance settings is ticked, and that the box alongside that is set to your required java version.