String에 char 추가하기

+) String+=char를 이용하는 방법

import java.util.*;
  
public class Main {
  public String solution(String str){
    String answer="";
    StringBuilder sb= new StringBuilder();
    char[] arr = str.toCharArray();
    for(char x : arr){
      if(Character.isLowerCase(x)) answer+=Character.toUpperCase(x);
      if(Character.isUpperCase(x)) answer+=Character.toLowerCase(x);
    }
    
    return answer;
  }
  public static void main(String[] args){
    Main T = new Main();
    Scanner kb=new Scanner(System.in);
    String str = kb.next();    
    
    System.out.println(T.solution(str));
  }
}

 

 

+) StringBuilder를 이용하는 방법

import java.util.*;
  
public class Main {
  public String solution(String str){
    String answer=" ";
    StringBuilder sb= new StringBuilder();
    char[] arr = str.toCharArray();
    for(char x : arr){
      if(Character.isLowerCase(x)) sb.append(Character.toUpperCase(x));
      if(Character.isUpperCase(x)) sb.append(Character.toLowerCase(x));
    }
    
    return answer=sb.toString();
  }
  public static void main(String[] args){
    Main T = new Main();
    Scanner kb=new Scanner(System.in);
    String str = kb.next();    
    
    System.out.println(T.solution(str));
  }
}