java-lamdba认知

1.实现Runnable

new Thread(() -> System.out.println(11)).start();

2.匿名内部类处理方式

public static void main(String[] args) {
   ww(() -> System.out.println("111"));
}
interface MM{
   void aa();
}
public static void ww(MM mm){
   mm.aa();
}

3.对列表操作（循环列表）

list.forEach(e -> System.out.println(e));

4.函数式编程（Predicate），and、or条件过滤

List<Integer> list = Arrays.asList(100, 200, 300, 400, 500);
Predicate<Integer> predicate1 = n -> n >= 100;
Predicate<Integer> predicate2 = n -> n < 300;
//与 或  .and  .or
list.stream().filter(predicate1.and(predicate2)).forEach(e-> System.out.println(e));

结果：
100
200

5.使用map，进行数据改变

List<Integer> list = Arrays.asList(100, 200, 300, 400, 500);
list.stream().map(cost -> cost + 10*cost).forEach(e-> System.out.println(e));

结果：
1100
2200
3300
4400
5500

注意：原来的list的值并没有改变

6.流API的 reduce() 方法将所有数字合成一个

List<Integer> costBeforeTax = Arrays.asList(100, 200, 300, 400, 500);
Integer result = costBeforeTax.stream().map(cost -> cost + 10*cost).reduce((sum,cost)-> sum + cost).get();
System.out.println(result);

结果：
16500

7.查询满足条件的list

List<Integer> costBeforeTax = Arrays.asList(100, 200, 300, 400, 500);
costBeforeTax = costBeforeTax.stream().filter(x-> x==100).collect(Collectors.toList());
System.out.println(costBeforeTax);

结果：
100

8.使用map，进行数据改变，并对数据拼接

List<String> list = Arrays.asList("a", "b", "c", "d");
String result = list.stream().map(e-> e.toUpperCase()).collect(Collectors.joining(","));
System.out.println(result);

结果：A,B,C,D

9.数据去重

   a.单个字段

List<Integer> numbers = Arrays.asList(9, 10, 3, 4, 9, 3, 4);
List<Integer> distinct = numbers.stream().distinct().collect(Collectors.toList());
System.out.println(numbers);
System.out.println(distinct);

结果：
[9, 10, 3, 4, 9, 3, 4]
[9, 10, 3, 4]

    b.对象

BookBo bookBo1 = new BookBo("1", "语文");
BookBo bookBo2 = new BookBo("2", "数学");
BookBo bookBo3 = new BookBo("3", "英语");
BookBo bookBo4 = new BookBo("4", "地理");
BookBo bookBo5 = new BookBo("5", "生物");
BookBo bookBo6 = new BookBo("1", "语文");
List<BookBo> bookBoList = Arrays.asList(bookBo1, bookBo2, bookBo3, bookBo4, bookBo5, bookBo6);

List<BookBo> distinctList = bookBoList
                .stream().collect(Collectors.collectingAndThen(Collectors.toCollection(()->new TreeSet<>(Comparator.comparing(o-> o.getName()))), ArrayList::new))
                .stream().sorted(Comparator.comparing(BookBo::getName)).collect(Collectors.toList());

System.out.println(distinctList);

结果：
[ BookBo{name='1', author='语文'},

  BookBo{name='2', author='数学'},

  BookBo{name='3', author='英语'},

  BookBo{name='4', author='地理'},

  BookBo{name='5', author='生物'}]

10.list转map

BookBo bookBo1 = new BookBo("1", "语文","a");
BookBo bookBo2 = new BookBo("2", "数学","b");
BookBo bookBo3 = new BookBo(null, "英语","c");
BookBo bookBo4 = new BookBo("4", "地理","d");
BookBo bookBo5 = new BookBo("5", "生物","e");
BookBo bookBo6 = new BookBo("6", "生物","f");
BookBo bookBo7 = new BookBo("7", "","g");
List<BookBo> bookBoList = Arrays.asList(bookBo1, bookBo2, bookBo3, bookBo4, bookBo5, bookBo6, bookBo7);
 //(k1,k2)-> k2  如果key值重复，取第二个
Map<String,BookBo> map = bookBoList.stream()
                .filter(x-> !StringUtils.isEmpty(x.getName()) && !StringUtils.isEmpty(x.getAuthor()))
                .collect(Collectors.toMap(k->k.getName()+"_"+k.getAuthor(), bookBo -> bookBo,(k1, k2)-> k2));
map.forEach((k,v)-> System.out.println(k+","+v));

结果：
1_语文,BookBo{name='1', author='语文', value='a'}
4_地理,BookBo{name='4', author='地理', value='d'}
2_数学,BookBo{name='2', author='数学', value='b'}
6_生物,BookBo{name='6', author='生物', value='f'}
5_生物,BookBo{name='5', author='生物', value='e'}

11.最大值、最小值、总和、平均值

List<Integer> primes = Arrays.asList(2, 3, null, 7, 11, 13, 17, 19, 23, 29);
IntSummaryStatistics stats = primes.stream().filter(e-> e!=null).mapToInt((x) -> x).summaryStatistics();
System.out.println(stats.getMax());
System.out.println(stats.getMin());
System.out.println(stats.getSum());
System.out.println(stats.getAverage());

结果：
29
2
124
13.777777777777779

12.排序

    a.单个字段排序

String[] atp = {"2016-06-28 08:00:00", "2017-12-05 19:17:32","2017-03-06 22:14:51","2016-12-28 08:00:00", "2017-03-05 19:17:32","2017-03-06 22:14:51"};
Arrays.sort(atp, Comparator.reverseOrder());
Arrays.asList(atp).forEach(System.out::println);
System.out.println("---");
Arrays.sort(atp, Comparator.naturalOrder());
Arrays.asList(atp).forEach(System.out::println);

结果：

2017-12-05 19:17:32
2017-03-06 22:14:51
2017-03-06 22:14:51
2017-03-05 19:17:32
2016-12-28 08:00:00
2016-06-28 08:00:00
---

2016-06-28 08:00:00
2016-12-28 08:00:00
2017-03-05 19:17:32
2017-03-06 22:14:51
2017-03-06 22:14:51
2017-12-05 19:17:32

    b.对象

BookBo bookBo1 = new BookBo("2", "语文","a");
BookBo bookBo2 = new BookBo(null, "数学","b");
BookBo bookBo3 = new BookBo("3", "英语","c");
BookBo bookBo4 = new BookBo("4", "地理","d");
BookBo bookBo5 = new BookBo("5", "生物","e");
BookBo bookBo6 = new BookBo("7", "生物","f");
BookBo bookBo7 = new BookBo("6", "","g");
List<BookBo> bookBoList = Arrays.asList(bookBo1, bookBo2, bookBo3, bookBo4, bookBo5, bookBo6, bookBo7);
//如果数据中有null，进行空处理 Comparator.nullsFirst(String::compareTo)
Collections.sort(bookBoList, Comparator.comparing(BookBo::getName, Comparator.nullsFirst(String::compareTo)));
bookBoList.forEach(e-> System.out.println(e));
System.out.println("--");
Collections.sort(bookBoList, Comparator.comparing(BookBo::getName, Comparator.nullsFirst(String::compareTo)).reversed());
bookBoList.forEach(e-> System.out.println(e));

结果：

BookBo{name='null', author='数学', value='b'}
BookBo{name='2', author='语文', value='a'}
BookBo{name='3', author='英语', value='c'}
BookBo{name='4', author='地理', value='d'}
BookBo{name='5', author='生物', value='e'}
BookBo{name='6', author='', value='g'}
BookBo{name='7', author='生物', value='f'}
--
BookBo{name='7', author='生物', value='f'}
BookBo{name='6', author='', value='g'}
BookBo{name='5', author='生物', value='e'}
BookBo{name='4', author='地理', value='d'}
BookBo{name='3', author='英语', value='c'}
BookBo{name='2', author='语文', value='a'}
BookBo{name='null', author='数学', value='b'}

 13.查询列表中，code=1的数据，返回第一个

        DeptKind deptKind = DeptKind.CFBDW;
        List<Dept> listDept = new ArrayList<>();
        Dept de = new Dept();
        de.setDeptKindId(2l);
        listDept.add(de);
        Optional<Dept> op = listDept.stream().filter(p -> deptKind.getCode().equals(p.getDeptKindId())).findFirst();
        //是否有值   这个一定要判断，如果不判断，数据不存在的情况下，会报错：No value present
        if(op.isPresent()){
            System.out.println(op.get().getDeptKindId());
        }

14.对列表的元素数据进行修改

ww.forEach(vo -> {vo.setEndDate(new Date());vo.setId(11l);});

15.返回列表中某个键的列表

List<Integer> list1 = list.stream().map(A::getId).collect(Collectors.toList());
List<Integer> list2 = list.stream().map(A::getAge).collect(Collectors.toList());//未去重
List<Integer> list3 = list.stream().map(A::getAge).distinct().collect(Collectors.toList());//已去重

16. list中，进行group by，得到结果

Map<String, Integer> collectTemp = list.stream().collect(Collectors.groupingBy(ForbidTypeAnalysisDto::getForbidTypeName, Collectors.summingInt(ForbidTypeAnalysisDto::getCount)));

collectTemp.forEach((key,value) -> System.out.println(key + "," + value));