为什么不通过引用更新此 HashMap 值？

Question

我想弄清楚为什么当引用更新时与 hashMap 关联的值没有更新。由于 Java 是 pass-by-value-by-reference，与 BIN1 关联的 value 不应该简单地指向现在 'curr 指向的新对象吗？

class Solution {
    static class Card{
        private final String bin;
        private final String cardType;
        private final String cardName;
        private int trustScore;

        public Card(String bin, String cardType, String cardName, int trustScore){
            this.bin = bin;
            this.cardType = cardType;
            this.cardName = cardName;
            this.trustScore = trustScore;
        }

        public String toString(){
            return this.bin + " " + this.cardName + " "+ this.cardType + " " + this.trustScore;
        }
    }
    static class CardProcessor{
        private Map<String, Card> map;

        CardProcessor(){
            this.map = new HashMap<>();
        }
        public void store(String bin, String cardType, String cardName, int trustScore){
            if(!map.containsKey(bin))
                map.put(bin, new Card(bin, cardType, cardName, trustScore));
            else {
                Card curr = map.get(bin);
                if(curr.trustScore < trustScore) {
                    curr = new Card(bin, cardType, cardName, trustScore);
                    map.put(bin, curr); // Why is this line necessary to point BIN1 to the new value of card? Since Curr is a reference to Card shouldn't curr simply point to the new value supplied?
                }
            }
        }
    }
    public static void main(String[] args) {
        CardProcessor cp = new CardProcessor();
        cp.store("BIN1", "VISA", "BoA", 1);
        cp.store("BIN1", "VIEX", "BACU", 5);
        System.out.println(cp.map.entrySet());
    }
}

Answer 1

首先您将 curr 指向 map.get(bin) 的结果：

Card curr = map.get(bin);

之后您将 curr 指向一个新对象：

curr = new Card(bin, cardType, cardName, trustScore);

map.get(bin)返回其引用的对象没有改变

map.get(bin).cardType = "VIEX"

会更改该对象中的内容。

为什么不通过引用更新此 HashMap 值？

Why isn't this HashMap value being updated via reference?

java

reference