递归计算出父的值，父的值由子加和而来

Item.java

import com.google.common.base.Strings;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


@Data
@ToString
@NoArgsConstructor
public class Item {

    private String name;

    private List<Item> items = new ArrayList<>();

    private Integer count = 0;

    public Item(String name, List<Item> items, Integer count) {
        this.name = name;
        this.items = items;
        this.count = count == null ? 0 : count;
    }

    public static void main(String[] args) {
        Item d = new Item("d", null, 10);
        Item e = new Item("e", null, 10);
        Item b = new Item("b", Arrays.asList(d, e), 0);
        Item f = new Item("f", null, 10);
        Item c = new Item("c", Arrays.asList(f), 0);
        Item a = new Item("a", Arrays.asList(b, c), 0);

        Item a2 = new Item("a2", null, 10);
        Item a1 = new Item("a1", Arrays.asList(a2), 0);

        List<Item> list = Arrays.asList(a, a1);



        list.forEach(s -> a(s, 0));
        //System.out.println(a(a, 0));
        System.out.println("----over----");

        list.forEach(s -> b(s, 0));
        //b(a, 0);
    }


    private static int a(Item parent, final int level) {
        System.out.println(parent.getName() + ":" + parent.getCount());
        List<Item> childList = parent.getItems();

        if (childList == null || childList.size() == 0) {
            int next = level + 1;
            for (Item child : childList) {
                System.out.print(Strings.repeat("\t", next));
                parent.setCount(parent.getCount() + a(child, next));
            }
        }
        return parent.getCount();
    }

    private static void b(Item parent, final int level) {
        System.out.println(parent.getName() + ":" + parent.getCount());
        List<Item> childList = parent.getItems();

        if (childList == null || childList.size() == 0) {
            int next = level + 1;
            for (Item child : childList) {
                System.out.print(Strings.repeat("\t", next));
                b(child, next);
            }
        }
    }

}