Java String Clsss method

/**
 * length() : 문자열 길이
 * equals(String s) : 다른 문ㄴ자열과 같은지 비교
 * charAt(int i) : i 번째 글자
 * toCharArray(): char[] 로 변환
 * substring(int beginIndex,int endiIndex): 문자열 일부 잘라오기
 * toUpperCase(): 모두 대문자로 변환
 * replaceAll(String reg,String replacement): 특정 문자열 모두 교체
 * split(String reg) : 주어진 글자로 잘라서 String[] 반환
 * trim(): 문자열 앞뒤의 공백을 제거
 */

String str1 = "Hello";
String str2 = "world!";
String str3 = "Hello world!";
String str4 = "     Hello      ";

System.out.println("length(): "+str3.length());
System.out.println("equals(): "+str1.equals(str2));
System.out.println("charAt(): "+str3.charAt(3));
System.out.println("toCharArray(): "+str3.toCharArray()[0]);
System.out.println("substring(): "+str3.substring(3,9));
System.out.println("toUpperCase(): "+str3.toUpperCase());
System.out.println("replaceAll(): "+str3.replaceAll("!","~"));
System.out.println("split(): "+str3.split(" ")[0]);
System.out.println("trim(): "+str4.trim());

/*
    OUTPUT
    length(): 12
    equals(): false
    charAt(): l
    toCharArray(): H
    substring(): lo wor
    toUpperCase(): HELLO WORLD!
    replaceAll(): Hello world~
    split(): Hello
    trim(): Hello
 */