[Stream] StreamApi

 @Test
 public void getStream(){
      String[] data = {"a","b"};
      // 获取一个串行（顺序）流
      Stream<String> stream = Arrays.stream(data);
      List<String> data1 = Arrays.asList(data);
      // 获取一个并行流
      Stream<String> stringStream = data1.parallelStream();
      // 串行流转并行流
      Stream<String> parallel = stream.parallel();
      // 通过Stream.of 获取stream,实际执行的是：Arrays.stream(values);
      Stream<Integer> integerStream = Stream.of(1, 2, 3, 4);
      // 无限流 迭代
      Stream.iterate(0 ,t ->t+1);
      // 无限流 生成
      Stream.generate(UUID::randomUUID).limit(10).forEach(System.out::println);
  }

@Test
 public void test01(){
     // 过滤 filter(Predicate<? super T> predicate)
     Stream<Integer> integerStream = Stream.of(1, 2, 3, 4);
     integerStream.filter(t -> t%2 ==0 ).forEach(System.out::print);
     System.out.println();
     // 截断
     Stream<Integer> integerStream1 = Stream.of(1, 2, 3, 4);
     integerStream1.limit(3).forEach(System.out::print);
     System.out.println();
     // 跳过 如果元素不足跳过个数，返回空stream
     Stream<Integer> integerStream2 = Stream.of(1, 2, 3, 4);
     integerStream2.skip(3).forEach(System.out::print);
     System.out.println();
     // 筛选去重 根据hashcode() 和equals() 对比去重
     Stream<Integer> integerStream3 = Stream.of(1, 2, 3, 4,2,1,1);
     integerStream3.distinct().forEach(System.out::print);
     System.out.println();
 }

 @Test
 public void test02(){
     // 映射 将元素准换成其他形式或提取信息，参数为函数，函数将会被应用到每一个元素，并映射成新的元素
    Stream<Integer> stream = Stream.of(1, 2, 3, 4,2,1,1);
    stream.map(val -> val * 10).forEach(System.out::print);
    System.out.println();
    List<DemoUser> demoUsers = Arrays.asList(new DemoUser("a", 10), new DemoUser("b", 20));
    Stream<String> stringStream = demoUsers.stream().map(DemoUser::getName);
    stringStream.forEach(System.out::print);
    System.out.println();
    // 映射 将元素准换成另一个流，参数为函数，函数将会被应用到每一个元素，并映连接成新的流
    Stream<Integer> stream1 = Stream.of(1, 2, 3, 4,2,1,1);
    Stream<Double> doubleStream = stream1.flatMap((val) -> Stream.of(val * 1.0));
    doubleStream.forEach(System.out::print);
    System.out.println();
}
@Data
@AllArgsConstructor
class DemoUser{
    private String name;
    private Integer age;
}

 @Test
  public void test() {
      // 自然排序，需要实现Comparable接口
      Stream<Integer> stream = Stream.of(1, 2, 3, 4,2,1,1);
      stream.sorted().forEach(System.out::print);
      System.out.println();
      // 比较器排序
      List<DemoUser> demoUsers = Arrays.asList(new DemoUser("a", 10), new DemoUser("b", 20));
      Stream<DemoUser> stringStream = demoUsers.stream().sorted( (u1, u2) -> u1.getAge().compareTo(u2.getAge()));
      stringStream.forEach(System.out::print);
  }

@Test
 public void test2() {
      // 匹配 allMatch 是否都满足条件
      Stream<Integer> stream = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream.allMatch(a -> a < 3));
      System.out.println();
      // 匹配 anyMatch 至少匹配一个元素
      Stream<Integer> stream1 = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream1.anyMatch(a -> a < 3));
      System.out.println();
      // 匹配 noneMatch 一个也没有匹配上
      Stream<Integer> stream2 = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream2.noneMatch(a -> a < 2));
      System.out.println();
      // 匹配 findFirst 返回第一个  Optional<T>
      Stream<Integer> stream3 = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream3.findFirst());
      System.out.println();
      // 匹配 findAny 返回任意一个  Optional<T>
      Stream<Integer> stream4 = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream4.findAny());
      System.out.println();
      // 匹配 count 返回总数
      Stream<Integer> stream5 = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream5.count());
      System.out.println();
      // 匹配 min 返回最小值
      Stream<Integer> stream6 = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream6.min((a,b) -> a.compareTo(b)));
      System.out.println();
      // 匹配 max 返回最大值
      Stream<Integer> stream7 = Stream.of(1, 2, 3, 4,2,1,1);
      System.out.println(stream7.max(Integer::compareTo));
      System.out.println();
      // 匹配 forEach 内部迭代
      Stream<Integer> stream8 = Stream.of(1, 2, 3, 4,2,1,1);
      stream8.forEach(System.out::println);
      System.out.println();
  }

@Test
public void test3() {
     // reduce 反复结合 返回 Object
     Stream<Integer> stream = Stream.of(1, 2, 3, 4, 2, 1, 1);
     System.out.println(stream.reduce(0,Integer::sum));// 反复累加 14
     System.out.println();
     // reduce 反复结合 返回 Optional
     Stream<Integer> stream1 = Stream.of(1, 2, 3, 4, 2, 1, 1);
     System.out.println(stream1.reduce(Integer::sum)); // 返回 Optional[14]
     System.out.println();
 }

@Test
public void test4() {
     // 收集到list
     Stream<Integer> stream = Stream.of(1, 2, 3, 4, 2, 1, 1);
     System.out.println(stream.collect(Collectors.toList())); //[1, 2, 3, 4, 2, 1, 1]
     System.out.println();
     // 收集到list
     Stream<Integer> stream1 = Stream.of(1, 2, 3, 4, 2, 1, 1);
     System.out.println(stream1.collect(Collectors.toSet())); //[1, 2, 3, 4]
     System.out.println();
 }