java - IndexOutOfBoundsException 即使元素存在于数组列表中

Question

我在 ArrayList 中有 10001 个元素，当我尝试将它们一一删除时，我在中途(即在 5000 个元素之后)收到 IndexOutOfBoundsException 异常。实在不知道为什么。

  public static void main(String[] args) {
    List<Integer> numberArrayList = new ArrayList<>();
    List<Integer> numberLinkedList = new LinkedList<>();

    long start, end;

    start = System.currentTimeMillis();
    for (int i = 0; i < 10_001; i++) {
      numberArrayList.add(i);
    }
    end = System.currentTimeMillis();

    System.out.println("Time taken to insert 10_001 elements in ArrayList: " + (end - start));

    start = System.currentTimeMillis();
    for (int i = 0; i < 10_001; i++) {
      numberLinkedList.add(i);
    }
    end = System.currentTimeMillis();

    System.out.println("Time taken to insert 10_001 elements in LinkedList: " + (end - start));

    /* **************************************************************/
    start = System.currentTimeMillis();
    for (int i = 0; i < 10_001; i++) {
      numberArrayList.remove(i);
    }
    end = System.currentTimeMillis();

    System.out.println("Time taken to remove 10_001 elements from the front in ArrayList: " + (end - start));

    start = System.currentTimeMillis();
    for (int i = 0; i < 10_001; i++) {
      numberLinkedList.remove(i);
    }
    end = System.currentTimeMillis();

    System.out.println("Time taken to remove 10_001 elements from the front in LinkedList: " + (end - start));


  }

上面的程序结果

Time taken to insert 100_001 elements in ArrayList: 2
Time taken to insert 100_001 elements in LinkedList: 1
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 5001, Size: 5000
    at java.util.ArrayList.rangeCheck(ArrayList.java:657)
    at java.util.ArrayList.remove(ArrayList.java:496)
    at collections_jnit.list.ArrayList_vs_LinkedList.main(ArrayList_vs_LinkedList.java:34)

Answer 1

一旦删除 5000 个元素，则意味着 10001-5000 = 5001，因此考虑从 0 开始索引，所以现在索引范围为 0 到 5000因此 5001 是异常(exception)。

解决方案:如果您想在遍历时从列表中删除项目，那么我建议使用迭代器

Iterator<Integer> itr = numberArrayList.iterator();
while (itr.hasNext()) {
    itr.remove();
}