Steam流--交易员和交易问题答案

public class DealTrans {
    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 brain = new Trader("Brain", "Cambridge");

        List<Transaction> transactions = Arrays.asList(
                new Transaction(brain, 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)
        );

        DealTrans dealTrans = new DealTrans();
        List<Transaction> list1 = dealTrans.function1(transactions);
        System.out.println("1------------------------------:");
        list1.forEach(System.out::println);

        List<String> list2 = dealTrans.function2(transactions);
        System.out.println("2------------------------------:");
        list2.forEach(System.out::println);

        List<Trader> list3 = dealTrans.function3(transactions);
        System.out.println("3------------------------------:");
        list3.forEach(System.out::println);

        List<String> list4 = dealTrans.function4(transactions);
        System.out.println("4------------------------------:");
        list4.forEach(System.out::println);

        boolean b5 = dealTrans.function5(transactions);
        System.out.println("5------------------------------:");
        System.out.println(b5);

        dealTrans.function6(transactions);

        int i7 = dealTrans.function7(transactions);
        System.out.println("7------------------------------:");
        System.out.println("Max:" + i7);

        Transaction t8 = dealTrans.function8(transactions);
        System.out.println("8------------------------------:");
        System.out.println(t8.toString());
    }

    /**
     * (1) 找出2011年发生的所有交易，并按交易额排序(从低到高)。
     * @param allTrans
     * @return
     */
    public List<Transaction> function1(List<Transaction> allTrans){
        return allTrans.stream()
                .filter(t -> t.getYear() == 2011)
                .sorted(Comparator.comparing(Transaction::getValue))
                .collect(toList());
    }

    /**
     * (2) 交易员都在哪些不同的城市工作过?
     * @param allTrans
     * @return
     */
    public List<String> function2(List<Transaction> allTrans){
        return allTrans.stream()
                .map(t -> t.getTrader().getCity())
                .distinct()
                .collect(toList());
    }

    /**
     * (3) 查找所有来自于剑桥的交易员，并按姓名排序。
     * @param allTrans
     * @return
     */
    public List<Trader> function3(List<Transaction> allTrans){
       return  allTrans.stream()
                .map(Transaction::getTrader)
                .filter(trader -> "Cambridge".equals(trader.getCity()))
                .distinct()
                .sorted(Comparator.comparing(Trader::getName))
                .collect(toList());
    }

    /**
     * （4）返回所有交易员的姓名字符串，按字母顺序排序。
     * @param allTrans
     * @return
     */
    public List<String> function4(List<Transaction> allTrans){
        return allTrans.stream()
                .map(t -> t.getTrader().getName())
                .distinct()
                .sorted()
                .collect(toList());
    }

    /**
     * (5) 有没有交易员是在米兰工作的?
     * @param allTrans
     * @return
     */
    public boolean function5(List<Transaction> allTrans){
        return allTrans.stream()
                .anyMatch(transaction -> "Milan".equals(transaction.getTrader().getCity()));
    }

    /**
     * (6) 打印生活在剑桥的交易员的所有交易额。
     * @param allTrans
     */
    public void function6(List<Transaction> allTrans){
        System.out.println("6------------------------------:");
        allTrans.stream()
                .filter(transaction -> "Cambridge".equals(transaction.getTrader().getCity()))
                .map(Transaction::getValue)
                .forEach(System.out::println);
    }

    /**
     * (7) 所有交易中，最高的交易额是多少?
     * @param allTrans
     * @return
     */
    public int function7(List<Transaction> allTrans){
        return allTrans.stream()
                .map(Transaction::getValue)
                .reduce(0, Integer::max);
    }

    /**
     * (8) 找到交易额最小的交易。
     * @param allTrans
     * @return
     */
    public Transaction function8(List<Transaction> allTrans){
         return allTrans.stream()
                 .min(Comparator.comparing(Transaction::getValue))
                 .orElse(null);
    }
}