List的分組，求和，過濾操作

package ---;


import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;

/**
 * Created by zhugenqi on 2018/9/18 0018.
 */
class ListToMap {
    private static List<Apple> appleList = new ArrayList<>();//存放apple對象集合;

    public static void main(String[] args) throws Exception {
        Apple apple1 = new Apple(1, "蘋果1", new BigDecimal("3.25"), 10);
        Apple apple12 = new Apple(1, "蘋果2", new BigDecimal("1.35"), 20);
        Apple apple13 = new Apple(2, "蘋果13", new BigDecimal("1.35"), 20);
        Apple apple2 = new Apple(2, "香蕉", new BigDecimal("2.89"), 30);
        Apple apple3 = new Apple(3, "荔枝", new BigDecimal("9.99"), 40);
        appleList.add(apple1);
        appleList.add(apple12);
        appleList.add(apple13);
        appleList.add(apple2);
        appleList.add(apple3);
        toMap(appleList);
    }

    private static void toMap(List<Apple> appleList) throws Exception {
        //轉化為map，並且對 key 去重
        Map<Integer, Apple> AppleMap = appleList.stream()
                           .collect(Collectors
                                   .toMap(Apple::getId, apple -> apple, (k1, k2) -> k1)
                                   );
        //根據分組
        Map<Integer, List<Apple>> AppleMap02 = appleList.stream().collect(Collectors.groupingBy(Apple::getId));

        //篩選出name為香蕉的code
        List<Apple> AppleMap03 = appleList.stream().filter(apple -> apple.getName().equals("香蕉")).collect(Collectors.toList());

        //分組求和
        BigDecimal TotalMoney = appleList.stream().map(Apple::getMoney).reduce(BigDecimal.ZERO, BigDecimal::add);

        BigDecimal sum = appleList.stream().filter(apple -> apple.getName().equals("香蕉")).map(Apple::getMoney).reduce(BigDecimal.ZERO,BigDecimal::add);

        //算出name的種類數量，並轉為set
        Set<String> names = appleList.stream().map(Apple::getName).collect(Collectors.toSet());

        System.out.println("主鍵去從");
        System.out.println(AppleMap);
        System.out.println("分組");
        for (Map.Entry entry : AppleMap02.entrySet()) {
            System.out.print(entry.getKey() + "   ");
            List list = (List) entry.getValue();
            for (Object object : list) {
                if (list.indexOf(object) > 0) {
                    System.out.print("    ");
                }
                System.out.println(object);
            }
        }
        System.out.println("過濾");
        System.out.println(AppleMap03);

        System.out.println("求和");
        System.out.println("總價格 ：" + TotalMoney);

        System.out.println("分組求和");
        System.out.println("總數量 ： " + sum);

        System.out.println("輸出種類");
        System.out.println("種類 ： "+names);
    }
}