Multiply Strings

//Multiply Strings Total Accepted: 33986 Total Submissions: 161757 My Submissions Question Solution 
//Given two numbers represented as strings, return multiplication of the numbers as a string.
//
//Note: The numbers can be arbitrarily large and are non-negative.
public class MultiplyStrings {


public static void main(String[] args) {
// TODO 自动生成的方法存根


}
public String multiply(String num1, String num2) {
   num1=new StringBuilder(num1).reverse().toString();
   num2=new StringBuilder(num2).reverse().toString();
   int[] d=new int[num1.length()+num2.length()];
   for(int i=0;i<num1.length();++i)
    //要细心 copy时多注意
    for(int j=0;j<num2.length();++j){
    d[i+j]=d[i+j]+(num1.charAt(i)-'0')*(num2.charAt(j)-'0');
    }
   StringBuilder sbBuilder=new StringBuilder();
   int ele;
   int carry=0;
   for(int i=0;i<d.length;++i){
    ele=(d[i]+carry)%10;
    carry=(d[i]+carry)/10;
    sbBuilder.insert(0, ele);
   
   }
   //注意出现0 先判断length长度
   while(sbBuilder.length()>0&&sbBuilder.charAt(0)=='0'){
    sbBuilder.deleteCharAt(0);
   }
   return sbBuilder.length()==0?"0":sbBuilder.toString();
}


}