Java流根据条件限制集合元素

Question

The below code, takes a stream, sorts it. If there is a maximum limit that should be applied, it would apply it.

if(maxLimit > 0) {
    return list.stream().sorted(comparator).limit(maxLimit).collect(Collectors.toList());
} else {
    return list.stream().sorted(comparator).collect(Collectors.toList());
}

//maxLimit, list, comparator can be understood in general terms.

Here, inside if, limit operation is present and in else, it is not present. Other operations on stream are same.

Is there any way to apply limit when maxLimit is greater than zero. In the code block presented above, same logic is repeated, except limit operation in one block.

Answer 1

You can split your code into parts like:

final Stream stream = list.stream()
        .sorted(comparator);

if (maxLimit > 0) {
    stream = stream.limit(maxLimit);
}

return stream.collect(Collectors.toList());

In this case you don't have to maintain two branches as it was in your initial example.

Also when assigning stream variable it's worth using specific generic type, eg if list is a List<String> then use Stream<String> type for a stream variable.

Answer 2

list.stream().sorted(comparator).limit(maxLimit>0 ? maxLimit: list.size()).collect(Collectors.toList())

查看当前的限制实施情况，我认为它会检查限制是否小于当前大小，因此不会像我最初预期的那样低效