@Before
public void init() {
 random = new Random();
 stuList = new ArrayList<Student>() {
 {
 for (int i = 0; i < 100; i++) {
 add(new Student("student" + i, random.nextInt(50) + 50));
 }
 }
 };
}
public class Student {
 private String name;
 private Integer score;
 //-----getters and setters-----
}
//1列出班上超过85分的学生姓名，并按照分数降序输出用户名字
@Test
public void test1() {
 List<String> studentList = stuList.stream()
 .filter(x->x.getScore()>85)
 .sorted(Comparator.comparing(Student::getScore).reversed())
 .map(Student::getName)
 .collect(Collectors.toList());
 System.out.println(studentList);
}

@Test
public void test1(){
 Stream<String> stream = Stream.generate(()->"user").limit(20);
 stream.forEach(System.out::println);
 stream.forEach(System.out::println);
}

public boolean filter(Student s) {
 System.out.println("begin compare");
 return s.getScore() > 85;
}
 
@Test
public void test() {
 Stream<Student> stream = Stream.of(stuArr).filter(this::filter);
 System.out.println("split-------------------------------------");
 List<Student> studentList = stream.collect(toList());
}

/**
 * 通过数组创建流
 */
@Test
public void testArrayStream(){
 //1.通过Arrays.stream
 //1.1基本类型
 int[] arr = new int[]{1,2,34,5};
 IntStream intStream = Arrays.stream(arr);
 //1.2引用类型
 Student[] studentArr = new Student[]{new Student("s1",29),new Student("s2",27)};
 Stream<Student> studentStream = Arrays.stream(studentArr);
 //2.通过Stream.of
 Stream<Integer> stream1 = Stream.of(1,2,34,5,65);
 //注意生成的是int[]的流
 Stream<int[]> stream2 = Stream.of(arr,arr);
 stream2.forEach(System.out::println);
}

/**
 * 通过集合创建流
 */
@Test
public void testCollectionStream(){
 List<String> strs = Arrays.asList("11212","dfd","2323","dfhgf");
 //创建普通流
 Stream<String> stream = strs.stream();
 //创建并行流
 Stream<String> stream1 = strs.parallelStream();
}

@Test
public void testEmptyStream(){
 //创建一个空的stream
 Stream<Integer> stream = Stream.empty();
}
4）创建无限流
@Test
public void testUnlimitStream(){
 //创建无限流，通过limit提取指定大小
 Stream.generate(()->"number"+new Random().nextInt()).limit(100).forEach(System.out::println);
 Stream.generate(()->new Student("name",10)).limit(20).forEach(System.out::println);
}

/**
 * 产生规律的数据
 */
@Test
public void testUnlimitStream1(){
 Stream.iterate(0,x->x+1).limit(10).forEach(System.out::println);
 Stream.iterate(0,x->x).limit(10).forEach(System.out::println);
 //Stream.iterate(0,x->x).limit(10).forEach(System.out::println);与如下代码意思是一样的
 Stream.iterate(0, UnaryOperator.identity()).limit(10).forEach(System.out::println);
}

/**
 * map把一种类型的流转换为另外一种类型的流
 * 将String数组中字母转换为大写
 */
@Test
public void testMap() {
 String[] arr = new String[]{"yes", "YES", "no", "NO"};
 Arrays.stream(arr).map(x -> x.toLowerCase()).forEach(System.out::println);
}

@Test
public void testFilter(){
 Integer[] arr = new Integer[]{1,2,3,4,5,6,7,8,9,10};
 Arrays.stream(arr).filter(x->x>3&&x<8).forEach(System.out::println);
}

/**
 * flapMap：拆解流
 */
@Test
public void testFlapMap1() {
 String[] arr1 = {"a", "b", "c", "d"};
 String[] arr2 = {"e", "f", "c", "d"};
 String[] arr3 = {"h", "j", "c", "d"};
 // Stream.of(arr1, arr2, arr3).flatMap(x -> Arrays.stream(x)).forEach(System.out::println);
 Stream.of(arr1, arr2, arr3).flatMap(Arrays::stream).forEach(System.out::println);
}

String[] arr1 = {"abc","a","bc","abcd"};
/**
 * Comparator.comparing是一个键提取的功能
 * 以下两个语句表示相同意义
 */
@Test
public void testSorted1_(){
 /**
 * 按照字符长度排序
 */
 Arrays.stream(arr1).sorted((x,y)->{
 if (x.length()>y.length())
 return 1;
 else if (x.length()<y.length())
 return -1;
 else
 return 0;
 }).forEach(System.out::println);
 Arrays.stream(arr1).sorted(Comparator.comparing(String::length)).forEach(System.out::println);
}
/**
 * 倒序
 * reversed(),java8泛型推导的问题，所以如果comparing里面是非方法引用的lambda表达式就没办法直接使用reversed()
 * Comparator.reverseOrder():也是用于翻转顺序，用于比较对象（Stream里面的类型必须是可比较的）
 * Comparator. naturalOrder()：返回一个自然排序比较器，用于比较对象（Stream里面的类型必须是可比较的）
 */
@Test
public void testSorted2_(){
 Arrays.stream(arr1).sorted(Comparator.comparing(String::length).reversed()).forEach(System.out::println);
 Arrays.stream(arr1).sorted(Comparator.reverseOrder()).forEach(System.out::println);
 Arrays.stream(arr1).sorted(Comparator.naturalOrder()).forEach(System.out::println);
}
/**
 * thenComparing
 * 先按照首字母排序
 * 之后按照String的长度排序
 */
@Test
public void testSorted3_(){
 Arrays.stream(arr1).sorted(Comparator.comparing(this::com1).thenComparing(String::length)).forEach(System.out::println);
}
public char com1(String x){
 return x.charAt(0);
}

@Before
 public void init(){
 arr1 = new String[]{"a","b","c","d"};
 arr2 = new String[]{"d","e","f","g"};
 arr3 = new String[]{"i","j","k","l"};
 }
 /**
 * limit，限制从流中获得前n个数据
 */
 @Test
 public void testLimit(){
 Stream.iterate(1,x->x+2).limit(10).forEach(System.out::println);
 }
 /**
 * skip，跳过前n个数据
 */
 @Test
 public void testSkip(){
// Stream.of(arr1).skip(2).limit(2).forEach(System.out::println);
 Stream.iterate(1,x->x+2).skip(1).limit(5).forEach(System.out::println);
 }
 /**
 * 可以把两个stream合并成一个stream（合并的stream类型必须相同）
 * 只能两两合并
 */
 @Test
 public void testConcat(){
 Stream<String> stream1 = Stream.of(arr1);
 Stream<String> stream2 = Stream.of(arr2);
 Stream.concat(stream1,stream2).distinct().forEach(System.out::println);
 }

@Before
public void init(){
 arr = new String[]{"b","ab","abc","abcd","abcde"};
}
/**
 * max、min
 * 最大最小值
 */
@Test
public void testMaxAndMin(){
 Stream.of(arr).max(Comparator.comparing(String::length)).ifPresent(System.out::println);
 Stream.of(arr).min(Comparator.comparing(String::length)).ifPresent(System.out::println);
}
/**
 * count
 * 计算数量
 */
@Test
public void testCount(){
 long count = Stream.of(arr).count();
 System.out.println(count);
}
/**
 * findFirst
 * 查找第一个
 */
@Test
public void testFindFirst(){
 String str = Stream.of(arr).parallel().filter(x->x.length()>3).findFirst().orElse("noghing");
 System.out.println(str);
}
/**
 * findAny
 * 找到所有匹配的元素
 * 对并行流十分有效
 * 只要在任何片段发现了第一个匹配元素就会结束整个运算
 */
@Test
public void testFindAny(){
 Optional<String> optional = Stream.of(arr).parallel().filter(x->x.length()>3).findAny();
 optional.ifPresent(System.out::println);
}
/**
 * anyMatch
 * 是否含有匹配元素
 */
@Test
public void testAnyMatch(){
 Boolean aBoolean = Stream.of(arr).anyMatch(x->x.startsWith("a"));
 System.out.println(aBoolean);
}
@Test
public void testStream1() {
 Optional<Integer> optional = Stream.of(1,2,3).filter(x->x>1).reduce((x,y)->x+y);
 System.out.println(optional.get());
}

@Test
 public void testOptional() {
 List<String> list = new ArrayList<String>() {
 {
 add("user1");
 add("user2");
 }
 };
 Optional<String> opt = Optional.of("andy with u");
 opt.ifPresent(list::add);
 list.forEach(System.out::println);
 }

@Test
public void testOptional2() {
 Integer[] arr = new Integer[]{4,5,6,7,8,9};
 Integer result = Stream.of(arr).filter(x->x>9).max(Comparator.naturalOrder()).orElse(-1);
 System.out.println(result);
 Integer result1 = Stream.of(arr).filter(x->x>9).max(Comparator.naturalOrder()).orElseGet(()->-1);
 System.out.println(result1);
 Integer result2 = Stream.of(arr).filter(x->x>9).max(Comparator.naturalOrder()).orElseThrow(RuntimeException::new);
 System.out.println(result2);
}

@Test
public void testStream1() {
 Optional<Student> studentOptional = Optional.of(new Student("user1",21));
 Optional<String> optionalStr = studentOptional.map(Student::getName);
 System.out.println(optionalStr.get());
}
public static Optional<Double> inverse(Double x) {
 return x == 0 ? Optional.empty() : Optional.of(1 / x);
}
public static Optional<Double> squareRoot(Double x) {
 return x < 0 ? Optional.empty() : Optional.of(Math.sqrt(x));
}
/**
 * Optional的迭代
 */
@Test
public void testStream2() {
 double x = 4d;
 Optional<Double> result1 = inverse(x).flatMap(StreamTest7::squareRoot);
 result1.ifPresent(System.out::println);
 Optional<Double> result2 = Optional.of(4.0).flatMap(StreamTest7::inverse).flatMap(StreamTest7::squareRoot);
 result2.ifPresent(System.out::println);
}

Student[] students;
@Before
public void init(){
 students = new Student[100];
 for (int i=0;i<30;i++){
 Student student = new Student("user",i);
 students[i] = student;
 }
 for (int i=30;i<60;i++){
 Student student = new Student("user"+i,i);
 students[i] = student;
 }
 for (int i=60;i<100;i++){
 Student student = new Student("user"+i,i);
 students[i] = student;
 }
}
@Test
public void testCollect1(){
 /**
 * 生成List
 */
 List<Student> list = Arrays.stream(students).collect(toList());
 list.forEach((x)-> System.out.println(x));
 /**
 * 生成Set
 */
 Set<Student> set = Arrays.stream(students).collect(toSet());
 set.forEach((x)-> System.out.println(x));
 /**
 * 如果包含相同的key，则需要提供第三个参数，否则报错
 */
 Map<String,Integer> map = Arrays.stream(students).collect(toMap(Student::getName,Student::getScore,(s,a)->s+a));
 map.forEach((x,y)-> System.out.println(x+"->"+y));
}
/**
 * 生成数组
 */
@Test
public void testCollect2(){
 Student[] s = Arrays.stream(students).toArray(Student[]::new);
 for (int i=0;i<s.length;i++)
 System.out.println(s[i]);
}
/**
 * 指定生成的类型
 */
@Test
public void testCollect3(){
 HashSet<Student> s = Arrays.stream(students).collect(toCollection(HashSet::new));
 s.forEach(System.out::println);
}
/**
 * 统计
 */
@Test
public void testCollect4(){
 IntSummaryStatistics summaryStatistics = Arrays.stream(students).collect(Collectors.summarizingInt(Student::getScore));
 System.out.println("getAverage->"+summaryStatistics.getAverage());
 System.out.println("getMax->"+summaryStatistics.getMax());
 System.out.println("getMin->"+summaryStatistics.getMin());
 System.out.println("getCount->"+summaryStatistics.getCount());
 System.out.println("getSum->"+summaryStatistics.getSum());
}

Student[] students;
@Before
public void init(){
 students = new Student[100];
 for (int i=0;i<30;i++){
 Student student = new Student("user1",i);
 students[i] = student;
 }
 for (int i=30;i<60;i++){
 Student student = new Student("user2",i);
 students[i] = student;
 }
 for (int i=60;i<100;i++){
 Student student = new Student("user3",i);
 students[i] = student;
 }
}
@Test
public void testGroupBy1(){
 Map<String,List<Student>> map = Arrays.stream(students).collect(groupingBy(Student::getName));
 map.forEach((x,y)-> System.out.println(x+"->"+y));
}
/**
 * 如果只有两类，使用partitioningBy会比groupingBy更有效率
 */
@Test
public void testPartitioningBy(){
 Map<Boolean,List<Student>> map = Arrays.stream(students).collect(partitioningBy(x->x.getScore()>50));
 map.forEach((x,y)-> System.out.println(x+"->"+y));
}
/**
 * downstream指定类型
 */
@Test
public void testGroupBy2(){
 Map<String,Set<Student>> map = Arrays.stream(students).collect(groupingBy(Student::getName,toSet()));
 map.forEach((x,y)-> System.out.println(x+"->"+y));
}
/**
 * downstream 聚合操作
 */
@Test
public void testGroupBy3(){
 /**
 * counting
 */
 Map<String,Long> map1 = Arrays.stream(students).collect(groupingBy(Student::getName,counting()));
 map1.forEach((x,y)-> System.out.println(x+"->"+y));
 /**
 * summingInt
 */
 Map<String,Integer> map2 = Arrays.stream(students).collect(groupingBy(Student::getName,summingInt(Student::getScore)));
 map2.forEach((x,y)-> System.out.println(x+"->"+y));
 /**
 * maxBy
 */
 Map<String,Optional<Student>> map3 = Arrays.stream(students).collect(groupingBy(Student::getName,maxBy(Comparator.comparing(Student::getScore))));
 map3.forEach((x,y)-> System.out.println(x+"->"+y));
 /**
 * mapping
 */
 Map<String,Set<Integer>> map4 = Arrays.stream(students).collect(groupingBy(Student::getName,mapping(Student::getScore,toSet())));
 map4.forEach((x,y)-> System.out.println(x+"->"+y));
}

DoubleStream doubleStream;
 IntStream intStream;
 /**
 * 原始类型流的初始化
 */
 @Before
 public void testStream1(){
 doubleStream = DoubleStream.of(0.1,0.2,0.3,0.8);
 intStream = IntStream.of(1,3,5,7,9);
 IntStream stream1 = IntStream.rangeClosed(0,100);
 IntStream stream2 = IntStream.range(0,100);
 }
 /**
 * 流与原始类型流的转换
 */
 @Test
 public void testStream2(){
 Stream<Double> stream = doubleStream.boxed();
 doubleStream = stream.mapToDouble(Double::new);
 }

public void peek1(int x) {
 System.out.println(Thread.currentThread().getName() + ":->peek1->" + x);
 }
 public void peek2(int x) {
 System.out.println(Thread.currentThread().getName() + ":->peek2->" + x);
 }
 public void peek3(int x) {
 System.out.println(Thread.currentThread().getName() + ":->final result->" + x);
 }
 /**
 * peek，监控方法
 * 串行流和并行流的执行顺序
 */
 @org.junit.Test
 public void testPeek() {
 Stream<Integer> stream = Stream.iterate(1, x -> x + 1).limit(10);
 stream.peek(this::peek1).filter(x -> x > 5)
 .peek(this::peek2).filter(x -> x < 8)
 .peek(this::peek3)
 .forEach(System.out::println);
 }
 @Test
 public void testPeekPal() {
 Stream<Integer> stream = Stream.iterate(1, x -> x + 1).limit(10).parallel();
 stream.peek(this::peek1).filter(x -> x > 5)
 .peek(this::peek2).filter(x -> x < 8)
 .peek(this::peek3)
 .forEach(System.out::println);
 }

/**
 * 生成一亿条0-100之间的记录
 */
@Before
public void init() {
 Random random = new Random();
 list = Stream.generate(() -> random.nextInt(100)).limit(100000000).collect(toList());
}
/**
 * tip
 */
@org.junit.Test
public void test1() {
 long begin1 = System.currentTimeMillis();
 list.stream().filter(x->(x > 10)).filter(x->x<80).count();
 long end1 = System.currentTimeMillis();
 System.out.println(end1-begin1);
 list.stream().parallel().filter(x->(x > 10)).filter(x->x<80).count();
 long end2 = System.currentTimeMillis();
 System.out.println(end2-end1);
 long begin1_ = System.currentTimeMillis();
 list.stream().filter(x->(x > 10)).filter(x->x<80).distinct().sorted().count();
 long end1_ = System.currentTimeMillis();
 System.out.println(end1-begin1);
 list.stream().parallel().filter(x->(x > 10)).filter(x->x<80).distinct().sorted().count();
 long end2_ = System.currentTimeMillis();
 System.out.println(end2_-end1_);
}

val count = sc.parallelize(1 to NUM_SAMPLES).filter { _ =>
 val x = math.random
 val y = math.random
 x*x + y*y < 1}.count()println(s"Pi is roughly ${4.0 * count / NUM_SAMPLES}")