如何在 SpringBoot 中添加 List 中元素的频率？

Question

This is my entity class and I am trying to show the frequency of elements as quantity but everytime I am getting 1 as quantity

@GeneratedValue(strategy = GenerationType.IDENTITY)
private int productid;
private String productname;
private String purchaseamount;
@Transient
private int quantity;

Here I am trying to get the quantity on the basis of frequency of elements of productId , but for every product I am getting 1 only

   public List<AddingProductForView> getData(List<Integer> productid) {
        List<AddingProductForView> findAllByProductIdIn = repository.findAllByproductidIn(productid);
        for (int i = 0; i < findAllByProductIdIn.size(); i++) {
            Set<Integer> distinct = new HashSet<>(productid);
            for (Integer count : distinct) {
                int frequency = Collections.frequency(productid, count);
                findAllByProductIdIn.get(i).setQuantity(frequency);
        
            }
        }
        return findAllByProductIdIn;
    }

RequestBody :- [1,1,1,1,2,2]

[
    {
        "productid": 1,
        "productname": "RO",
        "purchaseamount": "4000  ",
        "quantity": 1
    },
    {
        "productid": 2,
        "productname": "RO",
        "purchaseamount": "8000  ",
        "quantity": 1
    }
]

ExpectedResult:-

 [
        {
            "productid": 1,
            "productname": "RO",
            "purchaseamount": "4000  ",
            "quantity": 4
        },
        {
            "productid": 2,
            "productname": "RO",
            "purchaseamount": "8000  ",
            "quantity": 2
        }
    ]

Answer 1

I can understand your intention.
I try to this code my develop environment. It works very well.

I suggest some method

1.You had better debug

// whether frequency is exist or not.
int frequency = Collections.frequency(productid, count);

2.Do you want to this really? If this code excutes,Result of frequency is final entity of set.Because you don't use if condition.

for (int i = 0; i < findAllByProductIdIn.size(); i++) {
            //distinct = [1,2]
            Set<Integer> distinct = new HashSet<>(productid);
            /** frequency is unconditionally 2. */
            for (Integer count : distinct) {
                int frequency = Collections.frequency(productid, count);
                findAllByProductIdIn.get(i).setQuantity(frequency);
    
            }
    }

I can check frequency and getQuantity. I recommend to debug.

you are necessary if condition

loop : for (int i = 0; i < findAllByProductIdIn.size(); i++) {
            Set<Integer> distinct = new HashSet<>(productid);
            for (Integer count : distinct) {
                if(findAllByProductIdIn.get(i).getProductId == count) {
                    int frequency = Collections.frequency(productid, count);
                    findAllByProductIdIn.get(i).setQuantity(frequency);
                    continue loop;
                }
            }
        }

I modified your code. this is not necessary if condition and can reduce code line

for (int i = 0; i < findAllByProductIdIn.size(); i++) {
     int frequency = Collections.frequency(productid,findAllByProductIdIn.get(i).getProductId);
     findAllByProductIdIn.get(i).setQuantity(frequency);
}