stream流常用操作，当作笔记，有更好玩的再加！

package com.azure.stream;import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.*;
import java.util.stream.Collectors;public class ListCalculate {public static void main(String[] args) {List<Money> moneyList = getMoneyList();// List中的对象属性 求和int sumInt = moneyList.stream().mapToInt(Money::getAmountInt).sum();long sumLong = moneyList.stream().mapToLong(Money::getAmountLong).sum();double sumDouble = moneyList.stream().mapToDouble(Money::getAmountDouble).sum();BigDecimal sumBigDecimal = moneyList.stream().map(Money::getAmountBigDecimal).reduce(BigDecimal.ZERO, BigDecimal::add);// List中的对象属性 求最大值int maxInt = moneyList.stream().mapToInt(Money::getAmountInt).max().getAsInt();long maxLong = moneyList.stream().mapToLong(Money::getAmountLong).max().getAsLong();double maxDouble = moneyList.stream().mapToDouble(Money::getAmountDouble).max().getAsDouble();BigDecimal maxBigDecimal = moneyList.stream().map(Money::getAmountBigDecimal).reduce(BigDecimal.ZERO, BigDecimal::max);// List中的对象属性 求最小值  注意BigDecimalint minInt = moneyList.stream().mapToInt(Money::getAmountInt).min().getAsInt();long minLong = moneyList.stream().mapToLong(Money::getAmountLong).min().getAsLong();double minDouble = moneyList.stream().mapToDouble(Money::getAmountDouble).min().getAsDouble();BigDecimal minBigDecimal = moneyList.stream().map(Money::getAmountBigDecimal).reduce(BigDecimal.ZERO, BigDecimal::min);BigDecimal minBigDecimal2 = moneyList.stream().map(Money::getAmountBigDecimal).min(BigDecimal::compareTo).get();// List中的对象属性 求平均值double averageInt = moneyList.stream().mapToInt(Money::getAmountInt).average().getAsDouble();double averageLong = moneyList.stream().mapToLong(Money::getAmountLong).average().getAsDouble();double averageDouble = moneyList.stream().mapToDouble(Money::getAmountDouble).average().getAsDouble();BigDecimal averageBigDecimal = moneyList.stream().map(Money::getAmountBigDecimal).reduce(BigDecimal.ZERO, BigDecimal::add).divide(BigDecimal.valueOf(moneyList.size()), 2, RoundingMode.HALF_UP);// List中的对象属性 分组Map<String, List<Money>> map = moneyList.stream().collect(Collectors.groupingBy(Money::getType));System.out.println("===分组：===");map.forEach((k, v) -> System.out.println(k));// List中的对象属性 排序// 降序-递减List<Money> paiXuDesc = moneyList.stream().sorted(Comparator.comparing(Money::getAmountInt).reversed()).collect(Collectors.toList());// 升序-递增List<Money> paiXuAsc = moneyList.stream().sorted(Comparator.comparing(Money::getAmountInt)).collect(Collectors.toList());System.out.println("===排序：升序-递增===");paiXuAsc.forEach(list -> System.out.println(list.getAmountInt()));// 过滤System.out.println("===过滤：===");List<Money> guoLv = moneyList.stream().filter(list -> list.getAmountInt() == 123).collect(Collectors.toList());guoLv.forEach(list -> System.out.println(list.getType()));// 去重System.out.println("===去重：===");List<Money> quChoNg = moneyList.stream().distinct().collect(Collectors.toList());quChoNg.forEach(list -> System.out.println(list.getType()));// 分页System.out.println("===分页：===");int page = 2;int size = 3;List<Money> fenYe = moneyList.stream().skip((page - 1) * size).limit(size).collect(Collectors.toList());System.out.println(fenYe);// 转map：注意这里的key不要重复System.out.println("===转map：===");Map<String, Integer> listToMap = moneyList.stream().collect(Collectors.toMap(Money::getType, Money::getAmountInt));listToMap.forEach((k, v) -> {System.out.println(k);System.out.println(v);});// 取出某一字段数据System.out.println("===取出某一字段数据：===");List<String> typeList = moneyList.stream().map(Money::getType).collect(Collectors.toList());typeList.forEach(System.out::println);// 按某个字段分组（map无序，linkedMap有序）System.out.println("===按某个字段分组：===");List<List<Money>> newList = new ArrayList<>();moneyList.stream().collect(Collectors.groupingBy(Money::getType, LinkedHashMap::new, Collectors.toList())).forEach((k, v) -> newList.add(v));System.out.println(newList);}private static List<Money> getMoneyList() {List<Money> moneyList = new ArrayList<>();
//        moneyList.add(new Money("美金", 123, 741L, 369.85, new BigDecimal(321)));moneyList.add(new Money("美金", 123, 741L, 369.85, new BigDecimal(321)));moneyList.add(new Money("英镑", 456, 852L, 258.74, new BigDecimal(654)));
//        moneyList.add(new Money("英镑", 789, 963L, 147.96, new BigDecimal(987)));return moneyList;}
}class Money {private String type;private int amountInt;private long amountLong;private double amountDouble;private BigDecimal amountBigDecimal;public Money(String type, int amountInt, long amountLong, double amountDouble, BigDecimal amountBigDecimal) {this.type = type;this.amountInt = amountInt;this.amountLong = amountLong;this.amountDouble = amountDouble;this.amountBigDecimal = amountBigDecimal;}public String getType() {return type;}public void setType(String type) {this.type = type;}public int getAmountInt() {return amountInt;}public void setAmountInt(int amountInt) {this.amountInt = amountInt;}public long getAmountLong() {return amountLong;}public void setAmountLong(long amountLong) {this.amountLong = amountLong;}public double getAmountDouble() {return amountDouble;}public void setAmountDouble(double amountDouble) {this.amountDouble = amountDouble;}public BigDecimal getAmountBigDecimal() {return amountBigDecimal;}public void setAmountBigDecimal(BigDecimal amountBigDecimal) {this.amountBigDecimal = amountBigDecimal;}@Overridepublic String toString() {return "Money{" +"type='" + type + '\'' +", amountInt=" + amountInt +", amountLong=" + amountLong +", amountDouble=" + amountDouble +", amountBigDecimal=" + amountBigDecimal +'}';}
}