list遍历方法

List遍历方法

个人最常用的是增强for和stream流

• 简单for循环

          List<Integer> list = Arrays.asList(1, 2, 3, 4);
          AtomicInteger sum3 = new AtomicInteger();
          for (int i = 0; i < list.size(); i++) {
              sum += list.get(i);
          }
          System.out.println(sum);
  

• 增强for循环

          List<Integer> list = Arrays.asList(1, 2, 3, 4);
          int sum = 0;
          for (Integer integer : list) {
              sum += integer;
          }
          System.out.println(sum);
  

• 迭代器

          List<Integer> list = Arrays.asList(1, 2, 3, 4);
          int sum = 0;
          Iterator<Integer> iterator = list.iterator();
          while (iterator.hasNext()) {
              sum += iterator.next();
          }
          System.out.println(sum);
  

• stream流

          List<Integer> list = Arrays.asList(1, 2, 3, 4);
          int sum = 0;
          sum += list.stream().mapToInt(i -> i).sum();
          System.out.println(sum);
  

• foreach

  注意foreach的参数为Lambda表达式，变量必须为final

          List<Integer> list = Arrays.asList(1, 2, 3, 4);
          final int[] sum = {0};
          list.forEach(i -> sum[0] +=i);
          System.out.println(sum[0]);
  

          List<Integer> list = Arrays.asList(1, 2, 3, 4);
          AtomicInteger sum = new AtomicInteger();
          list.forEach(sum::addAndGet);
          System.out.println(sum);
  

思考

• stream流，引申出java8新特性的知识点
• foreach，引申出Lambda表达式和方法引用以及原子类操作知识点