8个Lambda表达式的练习题

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import static java.util.Comparator.comparing;
import static java.util.stream.Collectors.*;

public class Exercise {

    public static void main(String[] args) {
        Trader raoul = new Trader("Raoul", "Cambridge");
        Trader mario = new Trader("Mario", "Milan");
        Trader alan = new Trader("Alan", "Cambridge");
        Trader brian = new Trader("Brian", "Cambridge");

        List<Transaction> 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)
        );

        // 找出2011年发生的所有交易，并按交易额排序
        transactions.stream()
                .filter(tran -> 2011 == tran.getYear())
                .sorted(comparing(Transaction::getValue))
                .collect(Collectors.toList());

        // 交易员在哪些不同的城市工作过
        transactions.stream()
                .map(transaction -> transaction.getTrader().getName() + "---" + transaction.getTrader().getCity())
                .distinct()
                .collect(toList());

        // 查找所有来自剑桥的交易员，并按姓名排序
        transactions.stream()
                .map(Transaction::getTrader)
                .filter(trader -> "Cambridge".equals(trader.getCity()))
                .sorted(comparing(Trader::getName))
                .distinct()
                .collect(toList());

        // 返回所有交易员的姓名字符串，并按字母顺序排序
        String reduce = transactions.stream()
                .map(transaction -> transaction.getTrader().getName())
                .distinct()
                .sorted()
                .reduce("", (n1, n2) -> n1 + n2);

        // 有没有交易员在米兰工作的？
　　　　 // .anyMatch表示一组数据中,是否包含一条或多条该数据
        boolean anyMatch = transactions.stream()
                .anyMatch(transaction -> transaction.getTrader().getCity().equals("Milan"));
        System.out.println(anyMatch ? "有交易员在米兰" : "没有");

        // 打印生活在剑桥的交易员的所有交易额
        Map<String, Integer> cambridge = transactions.stream()
                .filter(transaction -> transaction.getTrader().getCity().equals("Cambridge"))
                .collect(groupingBy(transaction -> transaction.getTrader().getName(), summingInt(Transaction::getValue)));
        System.out.println(cambridge);

        // 所有交易中，最高的交易额是多少
        transactions.stream()
                .map(Transaction::getValue)
                .reduce(0, Integer::max);

        // 找到交易额最小的交易
        transactions.stream()
                .map(Transaction::getValue)
                .reduce(Integer::min).get();
    }
}