install java, update command

docker/Dockerfile

@@ -18,6 +18,7 @@ RUN apt-get -y install php7.2
 RUN apt-get -y install r-base
 RUN apt-get -y install mono-complete
 RUN apt-get -y install nasm
+RUN apt-get -y install openjdk-8-jre
 
 RUN useradd -m runner
 

docker/executors/java

@@ -1,5 +1,5 @@
-cp /*.code .
-name=$(cat $1 | grep -Eo 'public class ([A-Za-z0-9]+)' | cut -d' ' -f3)
-mv $1 $name.java
+cp /*.code interim.java
+name=$(cat interim.java | grep -Eo 'public class ([A-Za-z0-9]+)' | cut -d' ' -f3)
+mv interim.java $name.java
 timeout -s KILL 10 javac $name.java
 timeout -s KILL 3 java $name ${@:3}