String str="";
        for(String _s:s){
            str+=_s+",";
        }
        str=str.replaceAll("([0-9]{2})(?=[0-9])", "$1,");
        s=str.split(",");

------解决方案--------------------

循环递归就好：
Java code

    public static void main(String[] args) {
        String[] string = {"12","345","6789","0"};
        for(String s : string){
            substring(s);
        }
    }
    
    public static void substring(String s){
        String printString = null;
        if(s.length() > 2){
            printString = s.substring(0, 2);
            System.out.println(printString);
            substring(s.substring(2));
        }else{
            System.out.println(s);
        }
    }