递归实现一种字符串拼接方法

Question

递归实现叫做weave的方法, 可以将两个字符串相拼接,如果一个字符串比另一个长,就会拼接完后直接继续显示之后的字符,如果有null, 则throw illegalArgumentException,如果是空字符,则返回空字符.
如图所示

Answer 1

强行递归呀，哈哈哈

public class Demo {
    public static void main(String[] args) {
        String a = "aa";
        String b = "bbb";
        String wa = wa(a, b);
        System.out.println(wa);
    }

    private static String wa(String a,String b){
        String aa = "";
        if (a.length() !=0){
            aa = a.substring(0,1);
            a = a.replaceFirst(aa,"");
        }
        String bb = "";
        if (b.length() !=0){
            bb = b.substring(0,1);
            b = b.replaceFirst(bb,"");
        }
        if ( aa.length() == 0 && bb.length() == 0){
            return "";
        }
        return aa + bb + wa(a,b);
    }
}