stream,collection

array2list.java

            Integer[] array= new Integer[]{1,2,3};
            List<Integer> list = Arrays.asList(array);
            List<Integer> list2 = Arrays.asList(1,2,3);

collect-count.java

productList.stream()
  .collect(summingLong(Product::getGoodsNum));

// equals to                
productList.stream()
  .map(Product::getGoodsNum)
  .reduce(0L, (sumNum, num) -> sumNum += num);

ObjectList-toMap.java

        Map<Long, ShoppingCart> idAndCarts = curShoppingCarts.stream()
                .collect(Collectors.toMap(
                        ShoppingCart::getGoodsInfoId,
                        cart -> cart  // equal to  `identity()`
//                        ,
//                        (k, v) -> v
                ));