stream
老是打成 steam 哈哈哈(不是
主要针对集合或数组
https://www.runoob.com/java/java8-streams.html
简化集合或数组api的弊端
整成链式编程
常用api
- forEach:逐一遍历
- count:统计个数
- filter:过滤元素 就是匿名内部类Predicate,符合返回true
- limit:取前几个元素
- skip:跳过前几个
- map:加工方法
- concat:合并流
终结方法:
非终结方法:
收集 Stream 流:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138
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public class StreamTest { @Test public void test0(){ List<String> list = new ArrayList<>();
list.add("dd"); list.add("dwe"); list.add("dwq"); list.add("qd"); list.add("rd");
List<String> list_d = new ArrayList<>(); for (String s : list) { if (s.startsWith("d")){ list_d.add(s); } } System.out.println(list_d); List<String> list_d_3 = new ArrayList<>(); for (String s : list_d) { if (s.length() == 3){ list_d_3.add(s); } } System.out.println(list_d_3);
list.stream() .filter(s -> s.startsWith("d")) .filter(s -> s.length() == 3) .forEach(System.out::println);
long count = list.stream().count(); System.out.println(count);
list.stream() .filter(s -> s.length() == 3) .limit(2) .forEach(System.out::println);
list.stream() .filter(s -> s.length() == 3) .skip(2) .forEach(System.out::println);
list.stream().map(s -> s + "123").forEach(System.out::println);
list.stream().map(s -> new StreamPerson(s)).forEach(System.out::println); list.stream().map(StreamPerson::new).forEach(System.out::println);
Stream<Integer> s1 = Stream.of(1, 4, 3); Stream<String> s2 = list.stream(); Stream<Object> s1s2 = Stream.concat(s1, s2); s1s2.forEach(System.out::println);
Stream<String> stream = list.stream() .filter(s -> s.startsWith("d")) .filter(s -> s.length() == 3); Set<String> collect = stream.collect(Collectors.toSet());
Stream<String> stream1 = list.stream() .filter(s -> s.startsWith("d")) .filter(s -> s.length() == 3); List<String> collect1 = stream1.collect(Collectors.toList());
Stream<String> stream2 = list.stream() .filter(s -> s.startsWith("d")) .filter(s -> s.length() == 3); Object[] objects = stream2.toArray(); String[] strings = stream2.toArray(String[]::new); }
public static void main(String[] args) {
Collection<String> c = new ArrayList<>();
Stream<String> c_s = c.stream();
Map<String, Integer> map = new HashMap<>();
Stream<String> k_s = map.keySet().stream(); Stream<Integer> v_s = map.values().stream(); Stream<Map.Entry<String, Integer>> m_s = map.entrySet().stream();
String[] strings = {"ad", "dag", "dageae", "vcz"}; Stream<String> s_s = Arrays.stream(strings); Stream<String> s_s2 = Stream.of(strings);
} }
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