코딩테스트2번

import java.util.Scanner;
  
public class Main {
  
  public String solution(String str) {
		
		
		String ans  = "";
		
		for( int i = 0; i < str.length(); i ++) {
			
			if(Character.isUpperCase(str.charAt(i))) {
			ans += Character.toLowerCase(str.charAt(i));
				
			}else {
			ans +=	Character.toUpperCase(str.charAt(i));
			}
		}
		
		
		
		
		
		
		return ans;
	}
  
  
  public static void main(String[] args){
  	Main main = new Main();
	
	Scanner scan = new Scanner(System.in);
	
	String str = scan.next();
	
	System.out.println(main.solution(str));
  }
}

암기해야 할 부분

Character.isUpperCase(str.charAt(i)) -> true,false 반환