java - binary to decimal using CharAt( ) and length( ) -

ive written program converting binary decimal, wondering how can without using math.pow ( ) , using methods charat ( ) , length()

thank you,, appreciated

public class binarytodecimal{      public static void main(string[] args){         string binarystring = args[0];         int decimalvalue;          int length = binarystring.length();         double j = 0;          (int i=0; i< binarystring.length(); i++){             if (binarystring.charat(i)== '1'){                 j = j+  math.pow(2, binarystring.length() - 1 - i);             }         }          decimalvalue = (int) j;             system.out.println(decimalvalue);     } } 

you can try this:

int j = 0; (int i=0; i< binarystring.length(); i++) {   j <<= 1;   if (binarystring.charat(i)== '1')   {     ++j;   } }