Java接口RandomAccess全面了解

 if (list instance of RandomAccess) {
    for(int m = 0; m < list.size(); m++){}
  }else{
    Iterator iter = list.iterator();
    while(iter.hasNext()){}

  }

public class TestRandomAccess {
  @Test
  public void testTraverse() {
    ArrayList<Integer> arraylist = new ArrayList<Integer>();
    LinkedList<Integer> linkedList = new LinkedList<Integer>();
    initList(arraylist, 1000);
    initList(linkedList, 1000);

    System.out.println("ArrayList实现了RandomAccess接口");
    implRandomAccessTraverse(arraylist); //花了10ms时间
    System.out.println("LinkedList未实现了RandomAccess接口");
    implRandomAccessTraverse(linkedList); //花了434ms时间


    System.out.println("\nArrayList实现了RandomAccess接口");
    noImplRandomAccessTraverse(arraylist); //花了39ms时间
    System.out.println("LinkedList未实现了RandomAccess接口");
    noImplRandomAccessTraverse(linkedList); //花了27ms时间
  }

  private long startTime = 0;
  private long endTime = 0;
  // 初始化列表
  public void initList(List<Integer> list, int n) {
    for (int i = 0; i < n; i++) {
      list.add(i);
    }
  }

  //有实现RandomAccess接口的遍历全部数据,
  public void implRandomAccessTraverse(List list) {
    startTime = System.currentTimeMillis();
    for (int count = 0; count <= 1000; count++) {
      for (int i = 0; i < list.size(); i++) {
        list.get(i);
      }
    }
    endTime = System.currentTimeMillis();
    System.out.println("使用loop迭代一共花了" + (endTime - startTime) + "ms时间");
  }

  //没有实现RandomAccess接口的遍历全部数据
  public void noImplRandomAccessTraverse(List list) {
      startTime = System.currentTimeMillis();
      for (int count = 0; count <= 1000; count++) {
        for (Iterator itr = list.iterator(); itr.hasNext();) {
          itr.next();
        }
      }
      endTime = System.currentTimeMillis();
    System.out.println("使用Iterator迭代一共花了" + (endTime - startTime) + "ms时间");
  }

}