java - 如何用java迭代每n个元素？

Question

我有一个名为计算的方法，它需要很长时间才能完成。所以我决定将我的信息列表对象部分发送到此方法。如何迭代每 n 个元素？

public static void main(String [] args){
    Map<String, Long> info....;  //my info Map

    //I want to call method like 
    for(int i = 0; i<info.size(); i+=5)
       calculate(info.submap(i,i+5)); 
}


public static boolean calculate(Map<String, Long> info){
    //Some calculations

}

Answer 1

您可以使用以下代码

class SomeClass {

    private final int BUFFER_SIZE = 5;    

    public static void main(String[] args) {
        Map<String, Long> info = new HashMap<>();

        LongStream.range(0, 30).boxed().forEach(i -> info.put("key" + i, i)); // for test

        IntStream.range(0, info.size() / BUFFER_SIZE)
                .boxed()
                .parallel()
                .map(i -> Arrays.copyOfRange(info.keySet().toArray(), BUFFER_SIZE * i, BUFFER_SIZE * (i + 1)))
                .map(Arrays::asList)
                .map(keys -> info.entrySet().stream()
                        .filter(x -> keys.contains(x.getKey()))
                        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)))
                .forEach(SomeClass::calculate);
    }

    public static boolean calculate(Map<String, Long> info) {
        System.out.println("calculation for " + info.toString());
        return true;
    }
}