What is the fastest way to retrieve values from String?

Question

During my app development one performance question came to my mind:

I have a lot of lines of data that can looks like that:

• !ANG:-0.03,0.14,55.31
• !ANG:-0.03,-0.14,305.31
• !ANG:-234.03,-0.14,55.31
• in general: !ANG:float,float,float

Between those lines there are also "damaged" lines - they don't start with ! or are too short/have extra signs and so on.

To detect lines that are damaged at the begining I simply use

if(myString.charAt(0) != '!')//wrong string

What I can do to detect lines that are damaged at the end? It is very important to mention that I need not only to check if the line is correct but also get those 3 float numbers to use it later.

I've found three options for this:

• use regexp
• split twice (first ":" and second ",") and count elements
• use Scanner class

I am not sure which one of this (or maybe there are other) methods will be the best from the performance point of view. Can you please give me some advice?

EDIT:

After some comments I see that it is worth to write how damage lines an look:

• NG:-0.03,0.14,55.31
• .14,55.31
• !ANG:-0.03,0.14,
• !A,-0.02,-0.14,554,-0.12,55

It is quite difficult to talk about number of lines because I am getting them from readings from other device so I get packets of around 20 lines at a time with a frequency of 50Hz.

What I've found out so far is the big drawback of using scanner - for each line I need to create new object and after some time my device is starting to get short on resources.

Answer 1

Benchmark them, then you will know.

The likely fastest way is to write your own tiny state machine to match your format and find the float boundaries. Theoretically a regex will have the same performance, but it's likely to have additional overhead.

Answer 2

As an intermediate solution I'd do something like that :

private static class LineObject {
    private float f1, f2, f3;
}

private LineObject parseLine(String line) {
    LineObject obj = null;
    if (line.startsWith("!ANG:")) {
        int i = line.indexOf(',', 5);
        if (i != -1) {
            int j = line.indexOf(',', i+1);
            if (j != -1) {
                try {
                    obj = new LineObject();
                    obj.f1 = Float.parseFloat(line.substring(5, i));
                    obj.f2 = Float.parseFloat(line.substring(i+1, j));
                    obj.f3 = Float.parseFloat(line.substring(++j));
                } catch (NumberFormatException e) {
                    return null;
                }
            }
        }
    }
    return obj;
}

After you can copy/paste only usefull jdk code of startsWith, indexOf and parseFloat in your own state machine...