I follow all steps of the installation guide and when I try to open the omnet get this error: 
An error ha ocurred. See the log file Users/xxxX/omnetpp-5.2/ide/omnetpp.app/Contents/Eclipse/configuration/1509461950402.log 

The log file contains that:

```
!ENTRY org.eclipse.equinox.launcher 4 0 2017-10-31 16:19:02.116
!MESSAGE Exception launching the Eclipse Platform:
!STACK
java.lang.UnsupportedClassVersionError: org/eclipse/core/runtime/adaptor/EclipseStarter : Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(ClassLoader.java:637)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:621)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
    at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:650)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:590)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1499)

```