Java8-lambda-stream

实体类

1.Trader类

@Data
public class Trader{
    private final String name;
    private final String city;
}

2.Transaction类

@Data
public class Transaction {
    private final Trader trader;
    private final int year;
    private final int value;
}

3.初始化数据

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)
);

4.综合练习

• a查找2011年的所有交易，并按价值排序(从小到大)

List<Transaction> result = transactions.stream().filter(transaction -> transaction.getYear() == 2011)
                .sorted(Comparator.comparing(Transaction::getValue))
                .collect(toList());

• b商人工作的独特城市有哪些?

transactions.stream().map(t -> t.getTrader().getCity())
               .distinct().forEach(System.out::println);

• c找到所有来自剑桥的交易者，按名字排序。

transactions.stream().map(Transaction::getTrader)
                .filter(t -> t.getCity().equals("Cambridge"))
                .distinct()
                .sorted(Comparator.comparing(Trader::getName))
                .forEach(System.out::println);

• d 4.Return a string of all traders’ names sorted alphabetically

String value = transactions.stream().map(t -> t.getTrader().getName())
                .distinct()
                .sorted()
                .reduce("", (name1, name2) -> name1 + name2);
        System.out.println(value);

• e Are any traders based in Milan?

boolean liveInMilan1 = transactions.stream().anyMatch(t -> t.getTrader().getCity().equals("Milan"));
boolean liveInMilan2 = transactions.stream().map(Transaction::getTrader).anyMatch(t -> t.getCity().equals("Milan"));

//5. Are any traders based in Milan?

        boolean liveInMilan1 = transactions.stream().anyMatch(t -> t.getTrader().getCity().equals("Milan"));
        boolean liveInMilan2 = transactions.stream().map(Transaction::getTrader).anyMatch(t -> t.getCity().equals("Milan"));

        System.out.println(liveInMilan1);
        System.out.println(liveInMilan2);

        //6.Print all transactions’ values from the traders living in Cambridge.

        transactions.stream().filter(t -> t.getTrader().getCity().equals("Cambridge"))
                .map(Transaction::getValue)
                .forEach(System.out::println);


        //7.What’s the highest value of all the transactions?
        Optional<Integer> maxValue = transactions.stream().map(Transaction::getValue).reduce((i, j) -> i > j ? i : j);
        System.out.println(maxValue.get());

        //8.Find the transaction with the smallest value.
        Optional<Integer> minValue = transactions.stream().map(Transaction::getValue).reduce(Integer::min);
        System.out.println(minValue.get());