https://programmers.co.kr/skill_checks/331328

import java.util.Scanner;

class Solution {
    public boolean solution(String s) {
      boolean answer = true;
        
    	for(int i = 0; i < 4; i++){
        	String str = "";
        	if(i != s.length()-1) {
        		str = s.substring(i,i+1);
        	} else {
        		str = s.substring(s.length()-1);
        	}
        	Scanner scn = new Scanner(str);
        	if(!scn.hasNextInt()) {
        		answer = false;
        	}
        }   
        return answer;
    }    
}