[자바] 자바 외워두면 좋은 명령어 23가지 String : equals, indexOf, contains, charAt, replaceAll, substring, toUpperCase, split, join StringBuffer : append, insert, substring ArrayList : add, get, size, contains, remove Hashmap : put, get, containsKey, remove, size, keySet 즐거운프로그래밍 2023.11.09