How to sum occurrence elements count in java 8

Question

I want to find occurrence elements sum in java 8 and using my below technique i am getting all elements sum but i want to find only itemType=EQUIPMENT elements sum

Can some one help me please

double sum = itemList.stream().mapToDouble(a -> a.getQuantity())
                    .sum();

[
        {
            "itemType": "EQUIPMENT",
            "quantity": 6
        },
        {
            "itemType": "DTVN",
            "quantity": 2
        },
        {
            "itemType": "EQUIPMENT",
            "quantity": 1
        }
]

question from:https://stackoverflow.com/questions/65943035/how-to-sum-occurrence-elements-count-in-java-8

Answer 1

You can filter a particular itemType using equals or equalsIgnoreCase based on what you want

double sum = itemList.stream()
                .filter(type->"EQUIPMENT".equals(type.getItemType()))
                .mapToDouble(a -> a.getQuantity())
                .sum();