JavaEE进阶知识学习----Java8-4-2-StreamAPI

###StreamAPI练习
1.给定一个数字列表，返回一个由每一个数的平方构成的列表。

@Test
public void test(){
    Integer[] nums = new Integer[]{1,2,3,4,5};
    Arrays.stream(nums)
            .map((x) -> x*x)
            .forEach(System.out::println);

}

2.使用map和reduce方法数一数流中有多少个Employee

@Test
public void test1(){
  Optional<Integer> count = employees.stream()
           .map((e) -> 1)
           .reduce(Integer::sum);
  System.out.println(count.get());
}

####交易员类

public class Trader {

    private String name;
    private String city;

    public Trader() {
    }

    public Trader(String name, String city) {
        this.name = name;
        this.city = city;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    @Override
    public String toString() {
        return "Trader [name=" + name + ", city=" + city + "]";
    }

}

####交易类

public class Transaction {

    private Trader trader;
    private int year;
    private int value;

    public Transaction() {
    }

    public Transaction(Trader trader, int year, int value) {
        this.trader = trader;
        this.year = year;
        this.value = value;
    }

    public Trader getTrader() {
        return trader;
    }

    public void setTrader(Trader trader) {
        this.trader = trader;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    public int getValue() {
        return value;
    }

    public void setValue(int value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Transaction [trader=" + trader + ", year=" + year + ", value="
                + value + "]";
    }
}

####练习

public class TestTransaction {

    List<Transaction> transactions = null;

    @Before
    public void before(){
        Trader raoul = new Trader("Raoul", "Cambridge");
        Trader mario = new Trader("Mario", "Milan");
        Trader alan = new Trader("Alan", "Cambridge");
        Trader brian = new Trader("Brian", "Cambridge");

        transactions = Arrays.asList(
                new Transaction(brian, 2011, 300),
                new Transaction(raoul, 2012, 1000),
                new Transaction(raoul, 2011, 400),
                new Transaction(mario, 2012, 710),
                new Transaction(mario, 2012, 700),
                new Transaction(alan, 2012, 950)
        );
    }

    //1. 找出2011年发生的所有交易， 并按交易额排序（从低到高）
    @Test
    public void test1(){
        transactions.stream()
                .filter((t) -> t.getYear() == 2011)//过滤2011年的交易
                .sorted((t1,t2) -> Integer.compare(t1.getValue(),t2.getValue()))
                .forEach(System.out::println);
    }
    //2. 交易员都在哪些不同的城市工作过？
    @Test
    public void test2(){
        transactions.stream()
                .map((t) -> t.getTrader().getCity())
                .distinct()
                .forEach(System.out::println);
    }
    //3. 查找所有来自剑桥的交易员，并按姓名排序
    @Test
    public void test3(){
        new ArrayList<Integer>();
        transactions.stream()
                .filter((t) -> t.getTrader().getCity().equals("Cambridge"))
                .map(Transaction::getTrader)
                .sorted((t1,t2) -> t1.getName().compareTo(t2.getName()))
                .distinct()
                .forEach(System.out::println);
    }
    //4. 返回所有交易员的姓名字符串，按字母顺序排序
    @Test
    public void test4(){
        transactions.stream()
                .map((t) -> t.getTrader().getName())
                .sorted()
                .forEach(System.out::println);
        System.out.println("====================================");
        String str = transactions.stream()
                .map((t) -> t.getTrader().getName())
                .sorted()
                .reduce("",String::concat);
        System.out.println(str);
    }
    //5. 有没有交易员是在米兰工作的？
    @Test
    public void test5(){
        Boolean b1 = transactions.stream()
                .anyMatch((t) -> t.getTrader().getCity().equals("Milan"));
        System.out.println(b1);
    }
    //6. 打印生活在剑桥的交易员的所有交易额
    @Test
    public void test6(){
        Optional<Integer> sum = transactions.stream()
                .filter((e) -> e.getTrader().getCity().equals("Cambridge"))
                .map(Transaction::getValue)
                .reduce(Integer::sum);
        System.out.println(sum.get());
    }
    //7. 所有交易中，最高的交易额是多少
    @Test
    public void test7(){
        Optional<Integer> max = transactions.stream()
                .map((t) -> t.getValue())
                .max(Integer::compare);
        System.out.println(max);
    }
    //8. 找到交易额最小的交易
    @Test
    public void test8(){
        Optional<Transaction> op = transactions.stream()
                .min((t1,t2) -> Integer.compare(t1.getValue(),t2.getValue()));
        System.out.println(op.get());
    }
}