Binary representation of a real number

Given a real number between 0 and 7 (e.g., 0.72) that is passed in as a double, print the binary representation. If the number cannot be represented accurately in binary with at most 32 characters, print "ERROR."

Java代码：

public String printBinary(double num) {
        if((num <=0) ||(num>1))
            return "ERRORS";

        StringBuilder binary = new StringBuilder(".");

        while(num > 0) {
            if(binary.length()>=32)
                return "ERRORS";

            double r = 2*num;
            if(r>=1){
                binary.append("1");
                num = r -1;
            } else {
                binary.append("0");
                num = r;
            }
        }

      return binary.toString();
}