Lambda表達式集合操作

1、sort排序

根據某個對象字段屬性來排序對象

@Test

public void whenSortingEntitiesByName_thenCorrectlySorted() {

List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));

 

humans.sort((Human h1, Human h2) -> h1.getName().compareTo(h2.getName()));

Assert.assertThat(humans.get(0), equalTo(new Human("Jack", 12)));

}




反轉排序

@Test

public void whenSortingEntitiesByNameReversed_thenCorrectlySorted() {

    List<Human> humans = Lists.newArrayList(

      new Human("Sarah", 10), new Human("Jack", 12));

    Comparator<Human> comparator = (h1, h2) -> h1.getName().compareTo(h2.getName());

 

    humans.sort(comparator.reversed());

    Assert.assertThat(humans.get(0), equalTo(new Human("Sarah", 10)));

}







2、獲取某個對象集合中其中一個屬性的集合




List<Long> goodsIds = list.stream().map(CartListItemVO::getGoodsId).collect(Collectors.toList());




解釋：list：爲操作對象集合；

getGoodsId：要獲取的字段屬性

3、根據對象集合中某個屬性去掉對象集合中重複對象

List<VO> buildSeriesModels = list.stream()

                

.collect(Collectors.collectingAndThen(

                

        Collectors.toCollection(

                                () -> new TreeSet<>(Comparator.comparing(VO::getId))),

                        ArrayList::new));

4、字符串截取轉list(將字符串按#分割並轉爲list)

List<Long> seriesIds = Arrays.asList(seriesId.split("#")).stream().map(s -> Long.parseLong(s.trim()))

                   

 .collect(Collectors.toList());