StringBuilder的性能

1.新创建一个对象

  long startTimeA = System.currentTimeMillis();

  StringBuilder sb = null;
  for (int i = 1; i <= 10000000; i++) {
    sb = new StringBuilder();
    sb.append("1");
    String a = sb.toString();
  }

  this.newProject = System.currentTimeMillis() - startTimeA;

 

2.删除字符串

  long startTimeB = System.currentTimeMillis();

  for (int i = 1; i <= 10000000; i++) {

    sb.delete(0, sb.length());

    sb.append("2");

    String a = sb.toString();

  }

  this.delete = System.currentTimeMillis() - startTimeB;

 

3.设置长度

  long startTimeC = System.currentTimeMillis();

  for (int i = 1; i <= 10000000; i++) {

    sb.setLength(0);

    sb.append("3");

    String a = sb.toString();

  }

  this.updateLength = System.currentTimeMillis() - startTimeC;

 

运行结果:

newProject:168046

delete:95123

updateLength:93593

 

结论:可以明显看出,重新创建对象的方法是最慢的,删除字符串和设置长度的方法差别不大.