我如何在 Map 中存储多个键/值<string, deque<double> &gt; 一些变量名</string,>

Question

I am a beginner so please be easy on me. I have to create a Stocks program that would store different 3-letter stock codes, stock prices, and purchase prices. Then recall them to sell at a different price. The problem I am having is when I try to store my second stock, quantity, and price it deletes the first stock from the tree. If you need more of my code, please ask but here is my Map method for storing the keys and values:

    private String getPurchaseMap(String stockCode, Double quantityPurchased, Double purchasePrice) {
        Map<String, Deque<Block>> maintainStocks = new TreeMap<String, Deque<Block>>();
        var stock = new Block(stockCode, quantityPurchased, purchasePrice);
        var deque = new ArrayDeque<Block>();
        deque.offerFirst(stock);
        maintainStocks.put(stockCode, deque);
        var tempObj = maintainStocks.get(stockCode).peekFirst();
        for (var stocks : maintainStocks.entrySet()) {
            for (var test : stocks.getValue()) {
                System.out.printf("%s%n", stocks.getKey());
                System.out.println(tempObj.getQuantity());
                System.out.println(tempObj.getPrice());
            }
        }
            return null;
    }

Answer 1

Map.put method will replace the old value with new value for same key

Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for the key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.)

So you can use compute method in Map for adding the values to ArrayDeque which are having same key. If key doesn't exists than add create new ArrayDeque and value to it, If key already exists then add value to existing ArrayDeque

map.compute(key, (k, v) -> (v == null) ? new ArrayDeque<Block>() : v).offerFirst(stock);