标签：tip 实体 实体类 tostring names date find nba Collector
public class Trader {
private String name;
private String city;
public Trader(String n, String c) {
this.name = n;
this.city = c;
}
public String getName() {
return this.name;
}
public String getCity() {
return this.city;
}
public void setCity(String newCity) {
this.city = newCity;
}
public String toString() {
return "Trader:" + this.name + " in " + this.city;
}
}
Transaction.class
public class Transaction {
private Trader trader;
private int year;
private int value;
public Transaction(Trader trader, int year, int value) {
this.trader = trader;
this.year = year;
this.value = value;
}
public Trader getTrader() {
return this.trader;
}
public int getYear() {
return this.year;
}
public int getValue() {
return this.value;
}
public String toString() {
return "{" + this.trader + ", " +
"year: " + this.year + ", " +
"value:" + this.value + "}";
}
}
问题：
(1) 找出2011年发生的所有交易，并按交易额排序（从低到高）。 (2) 交易员都在哪些不同的城市工作过？ (3) 查找所有来自于剑桥的交易员，并按姓名排序。 (4) 返回所有交易员的姓名字符串，按字母顺序排序。 (5) 有没有交易员是在米兰工作的？ (6) 打印生活在剑桥的交易员的所有交易额。 (7) 所有交易中，最高的交易额是多少？ (8) 找到交易额最小的交易。
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import static java.util.Comparator.comparing;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.toList;
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 1: Find all transactions from year 2011 and sort them by value (small to high).
List<Transaction> tr2011 = transactions.stream()
.filter(transaction -> transaction.getYear() == 2011)
.sorted(comparing(Transaction::getValue))
.collect(toList());
System.out.println(tr2011);
// Query 2: What are all the unique cities where the traders work?
List<String> cities =
transactions.stream()
.map(transaction -> transaction.getTrader().getCity())
.distinct()
.collect(toList());
System.out.println(cities);
// Query 3: Find all traders from Cambridge and sort them by name.
List<Trader> traders =
transactions.stream()
.map(Transaction::getTrader)
.filter(trader -> trader.getCity().equals("Cambridge"))
.distinct()
.sorted(comparing(Trader::getName))
.collect(toList());
System.out.println(traders);
// Query 4: Return a string of all traders’ names sorted alphabetically.
String traderStr =
transactions.stream()
.map(transaction -> transaction.getTrader().getName())
.distinct()
.sorted()
.reduce("", (n1, n2) -> n1 + n2);
System.out.println(traderStr);
// 请注意，此解决方案效率不高（所有字符串都被反复连接，每次迭代的时候都要建立一个新的String对象）。
// 这里有一个更为高效的解决方案，它像下面这样使用joining（其内部会用到StringBuilder）：
String traderStr_2 =
transactions.stream()
.map(transaction -> transaction.getTrader().getName())
.distinct()
.sorted()
.collect(joining());
// Query 5: Are there any trader based in Milan?
boolean milanBased =
transactions.stream()
.anyMatch(transaction -> transaction.getTrader()
.getCity()
.equals("Milan")
);
System.out.println(milanBased);
// Query 6: Update all transactions so that the traders from Milan are set to Cambridge.
transactions.stream()
.map(Transaction::getTrader)
.filter(trader -> trader.getCity().equals("Milan"))
.forEach(trader -> trader.setCity("Cambridge"));
System.out.println(transactions);
// Query 7: What‘s the highest value in all the transactions?
int highestValue =
transactions.stream()
.map(Transaction::getValue)
.reduce(0, Integer::max);
System.out.println(highestValue);
// tips:流支持min和max方法，它们可以接受一个Comparator作为参数，指定计算最小或最大值时要比较哪个键值：
Optional<Transaction> smallestTransaction =
transactions.stream()
.min(comparing(Transaction::getValue));
}
}
标签：tip 实体 实体类 tostring names date find nba Collector
原文地址：https://www.cnblogs.com/sueyyyy/p/12142733.html
