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I just want to set a placeholder in a String to a running number in a big loop. For convenience the placeholder is %d. What is faster, using String's .format or .replace method?

GreenThor
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  • Have you tried both? What were your results? Is it possible to format the number to a fixed number of digits? (If so, creating a char array to reuse may well help...) Basically you haven't provided enough information here yet. A [mcve] showing what you've done so far, along with your concrete performance requirements, would really help. – Jon Skeet Dec 16 '16 at 09:59
  • @JonSkeet I was concentrating to much on coding and though just to throw this question into the room. I'm sorry I forgot about the guidelines, really need to think my questions through... – GreenThor Dec 16 '16 at 10:23

1 Answers1

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as I didn't know the response but I was curious about it I did a very simple test and add metrics and those are the results:

The code:

@Test
public void test(){
    String original = "This is the phrase %d";
    long init = System.currentTimeMillis();
    for(int i = 0; i < 100000; i++){
        System.out.println(String.format(original, i));
    }
    long end = System.currentTimeMillis();

    long init1 = System.currentTimeMillis();
    for(int i = 0; i < 100000; i++){
        System.out.println(original.replace("%d", String.valueOf(i)));
    }
    long end2 = System.currentTimeMillis();
    System.out.println("Method 1: " + (end-init));
    System.out.println("Method 2: " + (end2-init1));
}

The results

Method 1: 1950 Method 2: 1361

So we can assume .replace is faster than String's format method

cralfaro
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    Here's some reading http://stackoverflow.com/questions/504103/how-do-i-write-a-correct-micro-benchmark-in-java – Kayaman Dec 16 '16 at 10:10
  • @Kayaman thanks! is the best time i do a benchmark I will do next properly :) – cralfaro Dec 16 '16 at 10:14
  • I suspect there are far quicker options as well, working out where the format string is, and creating an appropriate `char[]`, then just replacing the relevant characters each time. – Jon Skeet Dec 16 '16 at 10:27