表示数字（Java）

JAVA

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        while(in.hasNext()){
            int flag = 0;
            StringBuilder sb = new StringBuilder();
            char[] arr = in.nextLine().toCharArray();
            for (int i = 0; i < arr.length; i++){
                if (isNumber(arr[i]) && flag == 0){
                    sb.append('*');
                    sb.append(arr[i]);
                    flag = 1;
                }else if (!isNumber(arr[i]) && flag == 1){
                    sb.append('*');
                    sb.append(arr[i]);
                    flag = 0;
                }else{
                    sb.append(arr[i]);
                }
            }
            if (isNumber(arr[arr.length - 1])) sb.append('*'); 
            System.out.println(sb.toString());
        }
    }
    private static boolean isNumber(char c){
        if (c >= '0' && c <= '9') {
            return true;
        }
        else {
            return false;
        }
    }
}