/** * StreamAPI的小练习 */public class StreamAPIExercise {    private List
     
       transactions;    @Before    public void before() {        Trader yan = new Trader("Yan", "Cambridge");        Trader zh = new Trader("ZH", "Milan");        Trader rose = new Trader("Rose", "Cambridge");        Trader lee = new Trader("Lee", "Cambridge");        transactions = Arrays.asList(new Transaction(yan, 2011, 300),                new Transaction(zh, 2012, 1000),                new Transaction(zh, 2011, 400),                new Transaction(rose, 2012, 710),                new Transaction(rose, 2012, 700),                new Transaction(lee, 2012, 950)        );    }    //给定一组数字的列表，返回由每个数字平方构成的列表    @Test    public void test1() {        Integer[] nums = new Integer[]{1, 2, 3, 4, 5};        Arrays.stream(nums).map((e) -> e * e).forEach(System.out::println);    }    //使用map reduce 方法数出流中有多少个Employee    @Test    public void test2() {        Optional
      
        sum = employees.stream().map(e -> 1).reduce(Integer::sum);        System.out.println(sum.get());    }    List
       
         employees = Arrays.asList(            new Employee("Yan", 18, '男', 0),            new Employee("Mike", 20, '女', 5000),            new Employee("Lee", 18, '女', 8000),            new Employee("Rose", 22, '男', 9000),            new Employee("Sk", 30, '男', 11000)    );    //找出2011年所有交易  并按照交易额排序（低->高）    @Test    public void test3() {        transactions.stream().filter((e) -> e.getYear() == 2011)                //.sorted((t1, t2) -> Integer.compare(t1.getValue(), t2.getValue()))                .sorted(new Comparator
        
         () {                    @Override                    public int compare(Transaction o1, Transaction o2) {                        return Integer.compare(o1.getValue(), o2.getValue());                    }                })                .forEach(System.out::println);    }    //交易员都在哪些不同城市工作过    @Test    public void test4() {        transactions.stream().map(t -> t.getTrader().getCity()).distinct().forEach(System.out::println);    }    //查找出来自剑桥的交易员，并按姓名排序    @Test    public void test5() {        transactions.stream().filter(t -> t.getTrader().getCity() == "Cambridge")                .map(t -> t.getTrader().getName())//                .sorted((t1, t2) -> t1.compareTo(t2))                .distinct()                .sorted(new Comparator
         
          () {                    @Override                    public int compare(String o1, String o2) {                        return o1.compareTo(o2);                    }                })                .forEach(System.out::println);    }    //返回所有交易员姓名的字符串，并按字母顺序排序    @Test    public void test6() {        transactions.stream().map(t->t.getTrader().getName())                .sorted().forEach(System.out::println);        System.out.println("------------------------------------------------");        //姓名连成一个字符串        System.out.println(transactions.stream().map(t -> t.getTrader().getName())                .sorted().reduce("", String::concat));        System.out.println("------------------------------------------------");        //姓名连成一个字符串 并按照字母排序  并且忽略大小写        //思路：1.取出集合中每个姓名  2.对每个姓名 取出所有字符 存入list集合  3.list.stream 将stream sorted排序        transactions.stream().map(t -> t.getTrader().getName())                .flatMap(StreamAPIExercise::filterCharacter)                .sorted((o1, o2) -> o1.compareToIgnoreCase(o2))                .forEach(System.out::print);    }    public static Stream
          
            filterCharacter(String str) { List
           
             list = new ArrayList<>(); for (Character ch : str.toCharArray()) { list.add(ch.toString()); } return list.stream(); } //有没有交易员在米兰工作 @Test public void test7() { boolean bl = transactions.stream().anyMatch(t -> t.getTrader().getCity() == "Milan"); } //打印剑桥的交易员所有交易额 @Test public void test8() { Optional
            
              sum = transactions.stream().filter(t -> t.getTrader().getCity().equals("Cambridge")) .map(t -> t.getValue()) .reduce((x,y)->Integer.sum(x,y)); // .reduce(Integer::sum); System.out.println(sum); } //所有交易中最高的交易额是多少 @Test public void test9() { Optional
             
               max = transactions.stream().map(t -> t.getValue()).max((x,y)->Integer.compare(x,y)); System.out.println(max.get()); } //找出最小交易 @Test public void test10() { Optional
              
                min = transactions.stream().min((x, y) -> Integer.compare(x.getValue(), y.getValue())); System.out.println(min.get()); }}