Question

I have this loop which splits a Boolean LinkedList by 8 bits and return the ASCII value of each byte in a buffer. The function return the string buffer.

This code is extremely slow if the LinkedList’s size is big. I try to change the Iterator with a simple looping, but it’s still slow.

How can this algorithm be really fast ? Maybe with multi-threading ?

Note: The size of the linkedList is not always divisible by 8.

public String toString(){

        String buffer = "";
        String output = "";

        LinkedList<Boolean> bits = this.bits;

        for(Iterator it = this.bits.iterator(); it.hasNext();){
            if(buffer.length() >= 8){
                output += (char)Integer.parseInt(buffer, 2);
                buffer = "";
            }

            buffer += ((Boolean)it.next() == false) ? "0" : "1";
        }

        if(buffer != "")
            output += (char)Integer.parseInt(buffer, 2);

        return output;
}

Answer 1

1. Use StringBuilder initialized with expected capacity for output:

   StringBuilder out = new StringBuilder(bits.size() / 8 + 1);
   

2. Use bitwise operations instead of parseInt(), something like this:

   int i = 0;          
   int c = 0;
   for(Boolean b: bits){
       if (i > 0 && i % 8 == 0){
           out.append((char) c);
           c = 0;
       }
       c = (c << 1) | (b ? 1 : 0);
       i++;
   }
   out.append((char) c); // Not sure about the desired behaviour here