You are lacking a class name:
public class myfile { ...
And lacks some basic programming practices. Should name your class MyFile
or so
import com.mongodb.MongoClient;
import com.mongodb.MongoException;
import com.mongodb.WriteConcern;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;
import com.mongodb.DBCursor;
import com.mongodb.ServerAddress;
import java.util.Arrays;
public class myfile {
DB db;
public myfile {
initDB();
}
public void initDB() {
MongoClient mongoclient = new MongoClient("localhost",27017);
db = mongoclient.getDB("test1");
}
...
}