lambda从地图检索整数

Question

I am trying to get the number after doing calculations using Lambda expression, but getting the error.

The lambda expression I am using:

int num = Optional.ofNullable(list.stream().filter(x->x.getType().getTypeId()==Type.getTypeId()).limit(1).map(x->x.getNum())).get();

After filtering, I want to get the first retrieved value. But I am getting the error as

cannot convert from Stream<Integer> to int

So, currently the way I am using is

Optional<> li = list.stream().filter(x->x.getType().getTypeId()==Type.getTypeId()).findFirst();
if (li.isPresent()) {
    num = li.map(x-> x.getNum()).get();
}

But, I was looking if the above could be done in a single line rather than extra if statement

Earlier, I tried the get() with findFirst() , but it was giving nullpointerException . How can I safely retrieve the value.

Answer 1

list.stream().filter(x->x.getType().getTypeId()==Type.getTypeId()).limit(1).map(x->x.getNum()) returns a Stream . You are lacking the findFirst terminal operation:

int num = 
    list.stream()
        .filter(x->x.getType().getTypeId()==Type.getTypeId())
        .map(x->x.getNum())
        .findFirst()
        .orElse(0); // default value in case the Stream is empty after the filtering