赵彬杰 :
I have the following data(A class structure):
[
{
"name": "a",
"enable": true
},
{
"name": "a",
"enable": false
},
{
"name": "b",
"enable": false
},
{
"name": "b",
"enable": false
},
{
"name": "c",
"enable": false
}
]
How can I replace the complex code below with a simple steam:
List<A> list = xxxxx;
Map<String, Integer> aCountMap = new HashMap<>();
list.forEach(item -> {
Integer count = aCountMap.get(item.getName());
if (Objects.isNull(count)) {
aCountMap.put(item.getName(), 0);
}
if (item.isEnable()) {
aCountMap.put(item.getName(), ++count);
}
});
The correct result is as follows:
{"a":1}
{"b":0}
{"c":0}
Naman :
You might simply be counting the objects filtered by a condition:
Map<String, Long> aCountMap = list.stream()
.filter(A::isEnable)
.collect(Collectors.groupingBy(A::getName, Collectors.counting()));
But since you are looking for the 0 count as well, Collectors.filtering with Java-9+ provides you the implementation such as :
Map<String, Long> aCountMap = List.of().stream()
.collect(Collectors.groupingBy(A::getName,
Collectors.filtering(A::isEnable,
Collectors.counting())));
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