Run build.sh with the environment variable J2OBJC set to your j2objc binary:
J2OBJC=~/j2objc/dist/j2objc ./build.sh javac compiled successfully translating outer/Outer.java error: outer/Outer.java:10: The import java.nio.file cannot be resolved Translated 0 files: 1 errors, 0 warnings Translated 0 methods as functions j2objc compilation failed