一次从数组10中提取项的最佳方法

Question

我有一个ArrayList，它可以包含无限数量的对象。我需要一次拉10个项目，并对它们进行操作。

我能想象的是这样做。

int batchAmount = 10;
for (int i = 0; i < fullList.size(); i += batchAmount) {
    List<List<object>> batchList = new ArrayList();
    batchList.add(fullList.subList(i, Math.min(i + batchAmount, fullList.size()));
    // Here I can do another for loop in batchList and do operations on each item
}

有什么想法吗？谢谢!

Answer 1

你可以这样做：

int batchSize = 10;
ArrayList<Integer> batch = new ArrayList<Integer>();
for (int i = 0; i < fullList.size();i++) {
    batch.add(fullList.get(i));
    if (batch.size() % batchSize == 0 || i == (fullList.size()-1)) {
        //ToDo Process the batch;
        batch = new ArrayList<Integer>();
    }
}

当前实现的问题是在每次迭代时都要创建一个batchList，需要在循环之外声明这个列表(batchList)。类似于：

int batchAmount = 10;
List<List<object>> batchList = new ArrayList();
for (int i = 0; i < fullList.size(); i += batchAmount) {
    ArrayList batch = new ArrayList(fullList.subList(i, Math.min(i + batchAmount, fullList.size()));
    batchList.add(batch);
 }
 // at this point, batchList will contain a list of batches

Answer 2

Guava library是由Google提供的，它方便了不同的功能。

List<Integer> countUp = Ints.asList(1, 2, 3, 4, 5);
List<Integer> countDown = Lists.reverse(theList); // {5, 4, 3, 2, 1}

List<List<Integer>> parts = Lists.partition(countUp, 2); // {{1, 2}, {3, 4}, {5}}

来自https://stackoverflow.com/a/9534034/3027124和https://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained#Lists的答案

希望这能有所帮助。

Answer 3

从ArrayList：ArrayList.remove(0)中提取元素

// clone the list first if you need the values in the future:
ArrayList<object> cloned = new ArrayList<>(list);
while(!list.isEmpty()){
    object[] tmp = new object[10];
    try{
        for(int i = 0; i < 10; i++) tmp[i] = list.remove(0);
    }catch(IndexOutOfBoundsException e){
        // end of list reached. for loop is auto broken. no need to do anything.
    }
    // do something with tmp, whose .length is <=10
}