Un exemple où il est plus rapide d'utiliser l'addition que d'utiliser StringBuilder (Java)

J'entends souvent dire qu'en Java, il est plus rapide d'utiliser StringBuilder au lieu de l'addition lors de la concaténation de chaînes, mais parfois ce n'est pas le cas. Exemple.

• Comme vous avez reçu Comment, c'était terriblement faux lors de sa première apparition. Excusez-moi. Même si les conditions correspondaient au code au moment de la première apparition, il n'y avait pas de différence, j'ai donc changé les conditions pour qu'il y ait une différence.

Environnement d'exécution

$ java --version
openjdk 12 2019-03-19
OpenJDK Runtime Environment (build 12+33)
OpenJDK 64-Bit Server VM (build 12+33, mixed mode, sharing)
$ javac --version
javac 12

Exemple de code 1

UseStringBuilder

UseStringBuilder.java

public class UseStringBuilder {
  private static int receiver(String s) {
    if (s.equals("hoge")) {
      return 1;
    } else {
      return 0;
    }
  }

  private static final String foo = "uprjkdowvyvqxlncsjgqzstikgclvgorshfrruifnnuzcfqtgtojfqsakcfvaisaysaxbrlpfczukomfxoebwypmqbkqmeevgivpdxnawthcazjobhhhydlbeiltwbmvwsykslyudqludjqlmkzilhreuxyajqgpiwebbxdnccrfmictdxolowxxnaeoucmtybdnmujrwshdezptpjpmzjdnasikhjztfnuezvipxwvywhgvmzqtrfehkkbrgganygop";
  private static final String bar = "bjsqdbkweettnvympybihyjrkhqtedvpogounxelthhyrtbpzoldujwzmmspacjtxwjwciusocwimihuumzvarvyqorunyinmqlkaefmlghcoxsvqbbazlbgavsffmqnjyaqturfgvwrfsgdcrksdexcipznpovpzilbgpxewclexahkxylffwsjiuiuthtbkrkqimcfcfzkoptzsroljeagdzgacdpgxdqwnjymwnnvqlohvsyxkbnazgedrxdjukfh";
  private static final String baz = "phblfiycdsnaahcskasevmthowdijgvfxdzuiivsubtqdwqzcbjhxvlhclkxnmpikfphceulcypiukpkrwzrnmzabydgmfwulrkjbonpcfgvjfbewdavycsjaqfsgvuqunblbzysezasrlrkeawotzjmdvemcqfditpjuolntiymrwxbgmhupoznjydqxzhghgifwnbkgosarjtuvxgneqorxzjemqtepwldrmqytkygsfetvnclqhyxoprioatxxkwo";
  private static final String qux = "rysvvsftwtolxonofdvkjjepouyayiyszgehjuqmunagaaiacrlpalcyizpwmrscldwpfiggobbsynzczfjhcqoqmlkvobljithjucwxmyzdsbrhkjpnpezxmqegbllwcdtraovdupkhbnsekkszffesmrpigwaeqqdxtnklusiwyljbhkzhktarxcraqvcvdybpunxeqnurmrbhoptgdffcfwwemqxvivxhgdnyttkivxjfzzhbqgujigmwmetnuxod";
  private static final String quux = "aodwvgukhmcwrzxwpmlucjnnwtjviytbtbahyexaefkmmweozifczxnzxafwbyjgoknssrtrdoihwhxmktsykfgapffmzqujlgtovsikgjwjtzcuxkgmequueqlnjratiqrznxpyomvsyiccbiyqrwbelbhpvvpgscqzpdsnqrohphdiomjcwivxddpyqelcdnapzlixbqdsfrehamzhyaavpuxjklllvulfqyostchdrgjgdbugfoeuknbsbrntkevf";

  public static void main(String[] args) {
    int sum = 0;
    String[] bars = new String[] { "baz", "qux" };
    for (int i = 0; i < Integer.parseInt(args[0]); ++i) {
      sum += receiver(new StringBuilder()
      .append("hoge")
      .append( foo )
      .append( bar )
      .append( baz )
      .append( qux )
      .append( quux )
      .toString() );
    }
    System.out.println(sum);
  }
}

UseStringPlus

UseStringPlus.java

public class UseStringPlus {
  private static int receiver( String s ){
    if ( s.equals("hoge") ){
      return 1;
    } else {
      return 0;
    }
  }
  private static final String foo = "uprjkdowvyvqxlncsjgqzstikgclvgorshfrruifnnuzcfqtgtojfqsakcfvaisaysaxbrlpfczukomfxoebwypmqbkqmeevgivpdxnawthcazjobhhhydlbeiltwbmvwsykslyudqludjqlmkzilhreuxyajqgpiwebbxdnccrfmictdxolowxxnaeoucmtybdnmujrwshdezptpjpmzjdnasikhjztfnuezvipxwvywhgvmzqtrfehkkbrgganygop";
  private static final String bar = "bjsqdbkweettnvympybihyjrkhqtedvpogounxelthhyrtbpzoldujwzmmspacjtxwjwciusocwimihuumzvarvyqorunyinmqlkaefmlghcoxsvqbbazlbgavsffmqnjyaqturfgvwrfsgdcrksdexcipznpovpzilbgpxewclexahkxylffwsjiuiuthtbkrkqimcfcfzkoptzsroljeagdzgacdpgxdqwnjymwnnvqlohvsyxkbnazgedrxdjukfh";
  private static final String baz = "phblfiycdsnaahcskasevmthowdijgvfxdzuiivsubtqdwqzcbjhxvlhclkxnmpikfphceulcypiukpkrwzrnmzabydgmfwulrkjbonpcfgvjfbewdavycsjaqfsgvuqunblbzysezasrlrkeawotzjmdvemcqfditpjuolntiymrwxbgmhupoznjydqxzhghgifwnbkgosarjtuvxgneqorxzjemqtepwldrmqytkygsfetvnclqhyxoprioatxxkwo";
  private static final String qux = "rysvvsftwtolxonofdvkjjepouyayiyszgehjuqmunagaaiacrlpalcyizpwmrscldwpfiggobbsynzczfjhcqoqmlkvobljithjucwxmyzdsbrhkjpnpezxmqegbllwcdtraovdupkhbnsekkszffesmrpigwaeqqdxtnklusiwyljbhkzhktarxcraqvcvdybpunxeqnurmrbhoptgdffcfwwemqxvivxhgdnyttkivxjfzzhbqgujigmwmetnuxod";
  private static final String quux = "aodwvgukhmcwrzxwpmlucjnnwtjviytbtbahyexaefkmmweozifczxnzxafwbyjgoknssrtrdoihwhxmktsykfgapffmzqujlgtovsikgjwjtzcuxkgmequueqlnjratiqrznxpyomvsyiccbiyqrwbelbhpvvpgscqzpdsnqrohphdiomjcwivxddpyqelcdnapzlixbqdsfrehamzhyaavpuxjklllvulfqyostchdrgjgdbugfoeuknbsbrntkevf";
  public static void main( String[] args ){
    int sum=0;
    String[] bars = new String[]{ "baz", "qux" };
    for( int i=0 ; i<Integer.parseInt(args[0]) ; ++i ){
      sum += receiver( 
        "hoge"
        + foo 
        + bar 
        + baz 
        + qux 
        + quux 
       );
    }
    System.out.println(sum);
  }
}

La personne qui court

run.rb

%w( UseStringBuilder UseStringPlus ).each do |name|
  p name
  puts( %x( javac #{name}.java && time java #{name} 10000000 ) )
end

Résultat d'exécution

"UseStringBuilder"

real	0m2.594s
user	0m2.488s
sys	0m0.356s
0
"UseStringPlus"

real	0m0.227s
user	0m0.239s
sys	0m0.036s
0

Exemple de code 2

Commentaire, et une expérience avec un échantillon qui ne se combine pas au moment de la compilation.

UseStringBuilder2

UseStringBuilder2.java

public class UseStringBuilder2 {
  private static int receiver(String s) {
    if (s.equals("hoge")) {
      return 1;
    } else {
      return 0;
    }
  }

  private static String makestr(int len, char c0){
    StringBuilder b = new StringBuilder();
    for( int i=0 ; i<len*1024 ; ++i ){
      b.append(c0+(char)i);
    }
    return b.toString();
  }

  public static void main(String[] args) {
    String foo = makestr(1, args[1].charAt(0));
    String bar = makestr(2, args[1].charAt(0));
    String baz = makestr(4, args[1].charAt(0));
    String qux = makestr(8, args[1].charAt(0));
    String quux = makestr(16, args[1].charAt(0));
    String corge = makestr(32, args[1].charAt(0));
    int sum = 0;
    String[] bars = new String[] { "baz", "qux" };
    for (int i = 0; i < Integer.parseInt(args[0]); ++i) {
      sum += receiver(new StringBuilder()
      .append("hoge")
      .append( foo )
      .append( bar )
      .append( baz )
      .append( qux )
      .append( quux )
      .append( corge )
      .toString() );
    }
    System.out.println(sum);
  }
}

UseStringPlus2

UseStringPlus2.java

public class UseStringPlus2 {
  private static int receiver( String s ){
    if ( s.equals("hoge") ){
      return 1;
    } else {
      return 0;
    }
  }
  private static String makestr(int len, char c0){
    StringBuilder b = new StringBuilder();
    for( int i=0 ; i<len*1024 ; ++i ){
      b.append(c0+(char)i);
    }
    return b.toString();
  }
  public static void main( String[] args ){
    String foo = makestr(1, args[1].charAt(0));
    String bar = makestr(2, args[1].charAt(0));
    String baz = makestr(4, args[1].charAt(0));
    String qux = makestr(8, args[1].charAt(0));
    String quux = makestr(16, args[1].charAt(0));
    String corge = makestr(32, args[1].charAt(0));
    int sum=0;
    for( int i=0 ; i<Integer.parseInt(args[0]) ; ++i ){
      sum += receiver( 
        "hoge"
        + foo 
        + bar 
        + baz 
        + qux 
        + quux 
        + corge
       );
    }
    System.out.println(sum);
  }
}

La personne qui court

%w( UseStringBuilder2 UseStringPlus2 ).each do |name|
  p name
  puts( %x( javac #{name}.java && time java #{name} 10000 a ) )
end

Résultat d'exécution

"UseStringBuilder2"

real	0m1.838s
user	0m1.608s
sys	0m0.450s
0
"UseStringPlus2"

real	0m0.917s
user	0m0.903s
sys	0m0.263s
0

alors

Ainsi, dans les cas ci-dessus, il est plus rapide de se connecter par addition.

Je pense qu'il y a diverses choses comme l'inversion selon la version Java.