java8 Lambda+stream 排序 选择 最大 最小 去重

1.交易员pojo

/*** @Author: donghai* @Description:* @Date: created on 2019/12/20  16:01*/
public class Trader {private final String name;private final 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;}@Overridepublic String toString(){return "Trader:"+this.name + " in " + this.city;}}

2.交易中心

/*** @Author: donghai* @Description:* @Date: created on 2019/12/20  16:02*/
public class Transaction {private final Trader trader;private final int year;private final 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;}@Overridepublic String toString(){return "{" + this.trader + ", " +"year: "+this.year+", " +"value:" + this.value +"}";}}

3.测试主类。所有注释都在这个类中，看代码即可！

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;import static java.util.stream.Collectors.joining;/*** @Author: donghai* @Description:* @Date: created on 2019/12/20  16:02*/
public class MainTrader {/*** 交易员和交易** @param args*/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));//1.找出2011年发生的所有交易，并按交易额排序（从低到高）。List<Transaction> collect = transactions.stream().filter(a -> a.getYear() == 2011).sorted(Comparator.comparing(Transaction::getValue)).collect(Collectors.toList());collect.forEach(a-> System.out.println(a.getYear()+":"+a.getValue()));//(2) 交易员都在哪些不同的城市工作过？Stream<String> distinct = transactions.stream().map(a -> a.getTrader().getCity()).distinct();distinct.forEach(a-> System.out.println(a));//(3) 查找所有来自于剑桥的交易员，并按姓名排序。List<Trader> cambridge = transactions.stream().filter(a -> a.getTrader().getCity().equals("Cambridge")).map(Transaction::getTrader).distinct().sorted(Comparator.comparing(Trader::getName)).collect(Collectors.toList());cambridge.forEach(a-> System.out.println(a.getName()));//(4) 返回所有交易员的姓名字符串，按字母顺序排序。---其内部会用到StringBuilderString reduce = transactions.stream().map(a -> a.getTrader().getName()).distinct().sorted().collect(joining());System.out.println(reduce);// collect.forEach(a-> System.out.println(a.getName()));//(5) 有没有交易员是在米兰工作的？boolean milan = transactions.stream().anyMatch(a -> a.getTrader().getCity().equals("Milan"));System.out.println(milan);//(6) 打印生活在剑桥的交易员的所有交易transactions.stream().filter(a -> a.getTrader().getCity().equals("Cambridge")).forEach(a-> System.out.println(a.getValue()));//(7) 所有交易中，最高的交易额是多少System.out.println( transactions.stream().map(Transaction::getValue).reduce(Integer::max));//(8) 找到交易额最小的交易System.out.println( transactions.stream().map(Transaction::getValue).reduce(Integer::min));//去重List<Long> userIdList = new ArrayList<>();userIdList.add(222L);userIdList.add(222L);userIdList.add(33L);userIdList.add(43L);List<Long> userIdFinalList = userIdList.stream().distinct().collect(Collectors.toList());userIdFinalList.forEach(aLong -> System.out.println(aLong));// removeif  删除 符合条件的 数据List<Integer> longList = new ArrayList<>();longList.add(1);longList.add(5);longList.add(9);longList.add(19);longList.add(30);longList.removeIf(a ->a > 5 && a < 30);longList.forEach(a ->System.out.println(a)););}
}