StringBuilderって速いの?

結論：ちょっぱや

import java.io.*;

class StringAppend {
  public static void main(String[] args) {
    for (int i=0 ; i<50 ; i+=5) {
      long start = System.currentTimeMillis();
      String str="";
      for (int j=0 ; j<100*(i+1) ; j++) {
        str += "aa";
      }
      System.out.println(""+i+" "+(System.currentTimeMillis()-start));
    }

    System.out.println("");

    for (int i=0 ; i<50 ; i+=5) {
      long start = System.currentTimeMillis();
      StringBuilder str= new StringBuilder();
      for (int j=0 ; j<100*(i+1) ; j++) {
        str.append("aa");
      }
      System.out.println(""+i+" "+(System.currentTimeMillis()-start));
    }
  }
}