我只是在玩Java 8 streams
并试图返回一串按字母顺序排序的所有交易者姓名。
public class PuttingIntoPractice {
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)
);
// Query 4: Return a string of all traders’ names sorted alphabetically.
String traderStr = transactions.stream()
.map(t -> t.getTrader().getName())
.sorted()
.reduce("", (n1, n2) -> n1 + n2);
System.out.println(traderStr);
}
}
我得到的输出如下所示:
AlanBrianMarioMarioRaoulRaoul
我想像下面这样显示
Alan Brian Mario Mario Raoul Raoul
我该怎么做?
我用龙目岛来生成所有这些样板的二传手吸气剂
@Setter @Getter
@ToString
@AllArgsConstructor
public class Trader {
private String name;
private String city;
}
交易
@Setter @Getter
@ToString
@AllArgsConstructor
public class Transaction {
private Trader trader;
private int year;
private int value;
}
代码中的问题是你如何减少Stream
。
正如目前所写,这个约简.reduce("", (n1, n2) -> n1 + n2);
将简单地连接 2 个String
,没有任何空格。要实现您想要的,您必须添加以将n1 + n2
更改为 n1 + " " + n2
.但是,由于您希望将Stream
的所有元素收集到单个String
中,因此您应该使用Collectors。
因此,应将代码更改为:
String traderStr = transactions.stream()
.map(t -> t.getTrader().getName())
.sorted()
.collect(Collectors.joining(" "));