2023-10-30 Today I Learned

오늘 개발한 것

https://greedydeveloper.tistory.com/87

[내일배움캠프][팀프로젝트]키오스크 개발일지

 

 

오늘 푼 문제

https://greedydeveloper.tistory.com/90

[프로그래머스]대소문자 바꿔서 출력하기

문제 풀면서 배운것

⭐Java에서 대소문자 바꿔서 출력하는 방법

String string = "aBcDeF"
string = string.toUpperCase();//ABCDEF
string = string.toLowerCase();//abcdef

⭐equalsIgnoreCase()

→ .equals()랑 똑같은 방법으로 사용, 대소문자는 무시하고 비교해준다

String str1 = "ABC"
String str2 = "abd"
str1.equalsIgnoreCase(str2)//true

예외처리 강의 들을때 matches본거 기억남

⭐String match()

String이 특정 패턴의 문자열을 포함하는지 확인할 수 있음

문자열에 정규표현식(regex)이 일치하는지를 boolean으로 리턴

String str = "my java test";

        //정확히 일치해야 true
        System.out.println( str.matches("java") );  // false
        System.out.println( str.matches("my java Test") );  // false (대/소문자 역시 구분한다.)
        System.out.println( str.matches("my java test") );  // true

        //정규표현식 사용-> 패턴이 맞으면 true
        System.out.println( str.matches(".*java.*") );  // true
        System.out.println( str.matches("(.*)test") );  // true

⭐Java Regular Expressions(Regex,정규표현식)

• Pattern Class - Defines a pattern (to be used in a search)
• Matcher Class - Used to search for the pattern
• PatternSyntaxException Class - Indicates syntax error in a regular expression pattern

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {
  public static void main(String[] args) {
    Pattern pattern = Pattern.compile("min", Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher("mintchoco");
    boolean matchFound = matcher.find();
    if(matchFound) {
      System.out.println("Match found");
    } else {
      System.out.println("Match not found");
    }
  }
}
// Outputs Match found

Match found

 

1. Pattern.compile() 메서드로 패턴이 만들어진다.

첫번째 parameter : 어떤 패턴이 찾아지는지 지정(필수)

두번째 parameter : case-insensitive 지정(선택)

 

2. matcher() 메서드가 문자열 안에서 패턴을 찾고 결과값을 담 Matcher object를 리턴한다

3. find() 메서드가 패턴이 발견되면 true를 발견되지 않았으면 false를 반환한다

Flags : flags in the compile() method

• Pattern.CASE_INSENSITIVE - The case of letters will be ignored when performing a search.
• Pattern.LITERAL - Special characters in the pattern will not have any special meaning and will be treated as ordinary characters when performing a search.
• Pattern.UNICODE_CASE - Use it together with the CASE_INSENSITIVE flag to also ignore the case of letters outside of the English alphabet

Pattern.compile()의 첫번째 parameter

⭐Regular Expression Patterns

[abc] Find one character from the options between the brackets

[^abc]	Find one character NOT between the brackets
[0-9]	Find one character from the range 0 to 9

⭐Metacharacters : characters with a special meaning

| | | Find a match for any one of the patterns separated by | as in: cat|dog|fish | | --- | --- | | . | Find just one instance of any character | | ^ | Finds a match as the beginning of a string as in: ^Hello | | $ | Finds a match at the end of the string as in: World$ | | \d | Find a digit | | \s | Find a whitespace character | | \b | Find a match at the beginning of a word like this: \bWORD, or at the end of a word like this: WORD\b | | \uxxxx | Find the Unicode character specified by the hexadecimal number xxxx |

⭐Quantifiers : Quantifiers define quantities

n+ Matches any string that contains at least one n

n*	Matches any string that contains zero or more occurrences of n
n?	Matches any string that contains zero or one occurrences of n
n{x}	Matches any string that contains a sequence of X n's
n{x,y}	Matches any string that contains a sequence of X to Y n's
n{x,}	Matches any string that contains a sequence of at least X n's

⭐Java String to Char array

// define a string
String vowels = "aeiou";

// create an array of characters 
char[] vowelArray = vowels.toCharArray();

// print vowelArray
System.out.println(Arrays.toString(vowelArray));