问生成包含两列筛选和求和数据的新列表

EN

List<Stock> resultingStocks = new ArrayList<>(allStock
        .stream()
        .collect(Collectors.toMap(st -> 
                        Arrays.asList(st.getStore(), st.getProductType()), 
                Function.identity(), 
                this::mergeStocks)) // explicit merging behaviour
        .values());

Stock mergeStocks(Stock stock1, Stock stock2) {
    return new Stock(stock1.getStore(), stock1.getProductType(), stock1
            .getAmount_1() + stock2.getAmount_1(), stock1.getAmount_2() + stock2.getAmount_2());
}

package ClassConcept;

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

public class stock {
    String s1,s2;
    int a1,a2;
    stock(String s1, String s2, int a1, int a2){
        this.s1 = s1;
        this.s2 = s2;
        this.a1 = a1;
        this.a2 = a2;

    }
}

public class ClassSpecifier {

    public static void main(String[] args) {

        List<stock> allStock = new ArrayList<>();

        allStock.add(new stock("l1", "CAIXA", 1, 4));
        allStock.add(new stock("l1", "CABIDE", 1, 0));
        allStock.add(new stock("l1", "CAIXA", 5, 5));
        allStock.add(new stock("l1", "CABIDE", 1, 0));

        allStock.add(new stock("l2", "CAIXA", 1, 4));
        allStock.add(new stock("l2", "CABIDE", 1, 0));
        allStock.add(new stock("l2", "CAIXA", 5, 5));
        allStock.add(new stock("l2", "CABIDE", 1, 1));

       // create a new list
        List<stock> allStockNew = new ArrayList<>();

        // now yo have to add your logic of adding multiple stock in this. you can use while or any condition as per your need

    // iterate through new list. if element present, add new value in this. else enter new entry.
        for(int i = 0 ; i < allStockNew.size() ; i++) {

            if (allStockNew.get(i).s2.euqals( "CAIXA") && allStockNew.get(i).s1.euqals( "l1")) {// your new stock name
                stock s = allStockNew.get(i);
                s.a1+=5;//new value
                s.a2+=5; // new value
                allStockNew.add(s);
            }
            else {
                allStockNew.add(new stock("l1", "CABIDE", 1, 0));
            }
        }

    }

}

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

/**
 * @Author Jack <jackkobec>
 */
public class Test {
    public static void main(String[] args) {

        List<Stock> allStock = new ArrayList<>();
        List<Stock> result = new ArrayList<>();

        allStock.add(new Stock("l1", "CAIXA", 1, 4));
        allStock.add(new Stock("l1", "CABIDE", 1, 0));
        allStock.add(new Stock("l1", "CAIXA", 5, 5));
        allStock.add(new Stock("l1", "CABIDE", 1, 0));

        allStock.add(new Stock("l2", "CAIXA", 1, 4));
        allStock.add(new Stock("l2", "CABIDE", 1, 0));
        allStock.add(new Stock("l2", "CAIXA", 5, 5));
        allStock.add(new Stock("l2", "CABIDE", 1, 1));

        allStock.stream().map(stock -> stock.productType).distinct()
                .forEach(distinctProductType -> {
                    allStock.stream().filter(stock -> stock.productType.equals(distinctProductType))
                            .reduce((stock1, stock2) -> {
                                if (stock1.store.equals(stock2.store)) {
                                    result.add(
                                            new Stock(
                                                    stock1.store,
                                                    stock1.productType,
                                                    stock1.amount_1 + stock2.amount_1,
                                                    stock1.amount_ + stock2.amount_));
                                }

                                return stock2;
                    });

                });

        result.forEach(stock -> System.out.println(
                "store: " + stock.store + "\n"
                + "productType: " + stock.productType + "\n"
                + "amount_1: " + stock.amount_1 + "\n"
                + "amount_: " + stock.amount_ + "\n"
        ));
    }
}

class Stock {
    public String store;
    public String productType;
    public Integer amount_1;
    public Integer amount_;

    public Stock() {
    }

    public Stock(String store, String productType, Integer amount_1, Integer amount_) {
        this.store = store;
        this.productType = productType;
        this.amount_1 = amount_1;
        this.amount_ = amount_;
    }

    @Override
    public String toString() {
        return "Stock{" +
                "store='" + store + '\'' +
                ", productType='" + productType + '\'' +
                ", amount_1=" + amount_1 +
                ", amount_=" + amount_ +
                '}';
    }
}