> Seems that you forgot to copy splitter.jar and fastutil.jar.

Sorry about that. You are right. Building mkgmap runs now without errors.

But

cd mkgmap/dist

java -Xmx5000m -cp mkgmap.jar:../lib/optional/* uk.me.parabola.mkgmap.sea.optional.PrecompSeaGenerator ../../land-polygons-split-4326/land_polygons.shp WGS84 ../../sea

still produces this error:

Exception in thread "main" java.lang.UnsupportedClassVersionError: uk/me/parabol

a/mkgmap/sea/optional/PrecompSeaGenerator : Unsupported major.minor version 51.0

        at java.lang.ClassLoader.defineClass1(Native Method)

        at java.lang.ClassLoader.defineClass(ClassLoader.java:634)

        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:14

2)

        at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)

        at java.net.URLClassLoader.access$000(URLClassLoader.java:73)

        at java.net.URLClassLoader$1.run(URLClassLoader.java:212)

        at java.security.AccessController.doPrivileged(Native Method)

        at java.net.URLClassLoader.findClass(URLClassLoader.java:205)

        at java.lang.ClassLoader.loadClass(ClassLoader.java:321)

        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)

        at java.lang.ClassLoader.loadClass(ClassLoader.java:266)

Could not find the main class: uk.me.parabola.mkgmap.sea.optional.PrecompSeaGene

rator. Program will exit.