将二进制字符串转换为ascii字符串很长一段时间（无API函数）

Question

I had an interview recently and discovered that I'd forgotten some of the basics. I've been playing around again and have written a function that will take a binary string (there is no validation yet) and returns the ascii representation of said string.

I'm looking for advice or tips on how it could be improved. I don't want to use any of the API functions, this is more of a playground scenario in which I might be able to learn something.

Thanks for any help.

Sample output:

01101000 01100101 01101100 01101100 01101111 
104
101
108
108
111
hello



public static String convertBinaryStringToString(String string){
    StringBuilder sb = new StringBuilder();
    char[] chars = string.replaceAll("\\s", "").toCharArray();
    int [] mapping = {1,2,4,8,16,32,64,128};

    for (int j = 0; j < chars.length; j+=8) {
        int idx = 0;
        int sum = 0;
        for (int i = 7; i>= 0; i--) {
            if (chars[i+j] == '1') {
                sum += mapping[idx];
            }
            idx++;
        }
        System.out.println(sum);//debug
        sb.append(Character.toChars(sum));
    }
    return sb.toString();
}

Answer 1

You don't need an array with the powers of two - the computer already knows them and you can use 1<<k to get the k-th power of two. However you don't need that either. Here is a short function to parse int from a char array that is the binary representation of a number. With a little modification the code will work for any base up to 10.

public static int parseBinary(char[] chars) {
  int res = 0;
  for (int i = 0; i < s.length; ++i) {
    res *= 2;
    if (chars[i] == '1') {
      res += 1;
    }
  }
  return res;
}

Using this function you can simplify your code significantly.

Answer 2

If you want a more java8-ish solution:

public static String convertBinaryStringToString(String string) {
    return stream(string.split("\\s+"))
            .mapToInt(s -> s.chars().reduce(0, (x, y) -> (char) (x * 2 + (y-'0'))))
            .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
            .toString();
}