＃-2020haoruo-example I am your teacher , HAORUO :OCJP ,who is a qualified Oracle Certified PROFESSIONAL Java Programmer . https://github.com/JavaOliverLu/java-daily/blob/master/ORACLE%20CERTIFIED%20PROFESSIONAL%20JAVA%20%20PROGRAMMER.pdf
https://github.com/JavaOliverLu/java-daily/blob/master/eCertificate.pdf