浅谈StringBuilder类的capacity()方法和length()方法的一些小坑

stringBuilder.delete(stringBuilder.capacity() - 5, stringBuilder.capacity());

StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("abcdefgh2321");
System.out.println("length:" + stringBuilder.length());
System.out.println("capacity:" + stringBuilder.capacity());
System.out.println("length截取：" + stringBuilder.delete(stringBuilder.length() - 3,stringBuilder.length()));
System.out.println("capacity截取：" + stringBuilder.delete(stringBuilder.capacity() - 7,stringBuilder.capacity()));
System.out.println("capacity截取：" + stringBuilder.delete(stringBuilder.capacity() - 5,stringBuilder.capacity()));

public class StringBuilderTest {
 public static void main(String[] args) throws Exception {
  // 前两行分别是获取运行次数和StringBuilder的初始化长度
  int times = args.length > 0 ? Integer.parseInt(args[0]) : 100;
  int length = args.length > 1 ? Integer.parseInt(args[1]) : 0;
  
  // 运行 times 次的 test(length)方法
  long t1 = System.currentTimeMillis();
  for (int i = 0; i < times; i++)
   test(length);
  long t2 = System.currentTimeMillis();
  
  // 输出单次运行时间 
  System.out.printf("Time taken: %d ms.\n", (t2 - t1) / times);
 }

 // 这个方法只是单纯地做循环向StringBuilder中添加数据。
 static int test(int length) {
  StringBuilder sb = new StringBuilder(length);
  for (int i = 0; i < 10000000; i++)
   sb.append(i + "");
  return sb.length();
 }
}