You need to increase the heap for the JVM. Add the following -Xmx1g -Xms1g when you run the import (or in your case the jar) e.g. java -Xmx1g -Xms1g ...
BTW: When using the graphhopper.sh you’d do
export JAVA_OPTS="-Xmx1g -Xms1g"
./graphhopper.sh import your.pbf