Java的stream流

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BigDecimal
        int 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;
    }

    @Override
    public String toString() {
        return "Money{" +
                "type='" + type + '\'' +
                ", amountInt=" + amountInt +
                ", amountLong=" + amountLong +
                ", amountDouble=" + amountDouble +
                ", amountBigDecimal=" + amountBigDecimal +
                '}';
    }
}