java8 集合神操作

Posted 2021-01-25 成长

　　

 1 public class StreamUtils {
 2 
 3     
 4 
 5     private static final List<Integer> listInteger = Lists.newArrayList(1, 2, 3, 4, 5, 6, 3, 5, 1, 4, 2, 8, 9);
 6 
 7     private static final List<Integer> arrayList = Lists.newArrayList(1, 25, 6, 9, 22, 44);
 8 
 9     public static void main(String[] args) {
10         ///取%2的数
11         List<Integer> collect = listInteger.stream().filter(i -> i % 2 == 0).collect(Collectors.toList());
12         System.out.println(collect);
13         ///去重
14         List<Integer> collect1 = listInteger.stream().distinct().collect(Collectors.toList());
15         System.out.println(collect1);
16 
17         ///跳过前面3个元素
18         List<Integer> collect2 = listInteger.stream().skip(3).collect(Collectors.toList());
19         System.out.println(collect2);
20 
21         ///取前面3个元素
22         List<Integer> collect3 = listInteger.stream().limit(3).collect(Collectors.toList());
23         System.out.println(collect3);
24 
25         ///打印dish getName集合
26         List<String> collect4 = list.stream().map(Dish::getName).collect(Collectors.toList());
27         System.out.println(collect4);
28 
29         String[] helloWord = {"hellow", "word"};
30         ///{h,e,l,l,o,w},{w,o,r,d}
31         Stream<String[]> stream = Arrays.stream(helloWord).map(s -> s.split(""));
32         ///h,e,l,l,o,w,w,o,r,d || flatMap 扁平化操作接受stream
33         Stream<String> stringStream = stream.flatMap(Arrays::stream);
34         ///去重
35         stringStream.distinct().forEach(System.out::println);
36         //allMatch 所有的元素的满足条件
37         System.out.println(arrayList.stream().allMatch(i -> i > 50));
38 
39         ///anyMatch 当元素数组中有一个元素满足就返回true
40         System.out.println(arrayList.stream().anyMatch(i -> i > 40));
41 
42         ///noneMatch 没有一个元素满足的情况下返回true
43         System.out.println(arrayList.stream().noneMatch(i -> i < 0));
44 
45         ///findAny随机获取一个元素
46         Optional<Integer> any = arrayList.stream().filter(i -> i > 2).findAny();
47         System.out.println(any.get());
48 
49         ///Options 中的orElse 如果返回结果是null使用orElse可以设置默认值,返回-1
50         Integer integer = arrayList.stream().filter(i -> i > 66).findAny().orElse(-1);
51         System.out.println(integer);
52 
53         ///isPresent元素是否存在,ifPresent 元素存在需要做什么事情
54         Optional<Integer> first = arrayList.stream().filter(i -> i > 10).findFirst();
55         System.out.println("optional元素是否存在:"+first.isPresent());
56         first.ifPresent(System.out::println);
57 
58         //reduce 聚合函数 将数组中的元素累加  0设置默认值初始值
59         Integer sum = arrayList.stream().reduce(0, (x, y) -> x + y);
60         System.out.println(sum);
61 
62         ///打印数组中累加的值
63         arrayList.stream().reduce((x,y)->x+y).ifPresent(System.out::println);
64 
65         ///获取数组中的最大值
66         System.out.println(arrayList.stream().reduce(Integer::max).get());
67         ///获取数组最小值
68         System.out.println(arrayList.stream().reduce(Integer::min).get());
69 
70         ///累加
71         arrayList.stream().reduce(Integer::sum).ifPresent(System.out::println);
72 
73
74     }
75 }