如何将嵌套列表转换为多维数组? [英] How to convert nested List into multidimensional array?
问题描述
在 Java 中,我想将嵌套的 List
转换为该类型的多维数组,其中包含最深层的统一类型.例如,将 ArrayList
转换为 String[][][][]
.我尝试了几件事,但我只能获得像 Object[][][][]
这样的对象数组.对于简单列表",似乎 Apache Commons Lang 可以完成这项工作,但我无法弄清楚嵌套的情况.
In Java I want to convert a nested List
which contains at the deepest level a uniform type into an multidimensional array of that type. For example, ArrayList<ArrayList<ArrayList<ArrayList<String>>>>
into String[][][][]
. I've tried several things and I only can obtain an array of objects like Object[][][][]
. For 'simple lists' it seems that Apache Commons Lang does the work but I cannot figure out for nested cases.
更新:
为了获得对象类型的多维数组,我使用了递归函数,因此无法使用 toArray() 设置键类型,请参阅摘录:
In order to obtain a multidimensional array of Object type I'm using a recursive function so I cannot set the key type using toArray() see excerpt:
// the argument of this function is a (nested) list
public static Object convert(Object object) {
Object[] result = null;
List list = (List) object;
if (list != null) {
Object type = getElementType(list);
if (type instanceof List) {
int size = list.size();
result = new Object[size];
for (int counter = 0; counter < size; counter++) {
Object element = list.get(counter);
result[counter] = (element != null) ? convert(element) : null;
}
} else {
result = list.toArray();
}
}
return result;
}
private static Object getElementType(List list) {
Object result = null;
for (Object element : list) {
if (element != null) {
result = element;
break;
}
}
return result;
}
推荐答案
这是有人建议解决String
类型的方法.Cast2(List>)
返回多维数组.可以推广使用类类型作为参数.感谢您的评论.
This is the way that someone suggested to solved for String
type. Cast2(List<?>)
returns the multidimensional array. It may be generalized to use the class type as parameter. Thank you for your comments.
static int dimension2(Object object) {
int result = 0;
if (object instanceof List<?>) {
result++;
List<?> list = (List<?>) object;
for (Object element : list) {
if (element != null) {
result += dimension2(element);
break;
}
}
}
return result;
}
static Object cast2(List<?> l) {
int dim = dimension2(l);
if (dim == 1) {
return l.toArray(new String[0]);
}
int[] dims = new int[dimension2(l)];
dims[0] = l.size();
Object a = Array.newInstance(String.class, dims);
for (int i = 0; i < l.size(); i++) {
List<?> e = (List<?>) l.get(i);
if (e == null) {
Array.set(a, i, null);
} else if (dimension2(e) > 1) {
Array.set(a, i, cast2(e));
} else {
Array.set(a, i, e.toArray(new String[0]));
}
}
return a;
}
这篇关于如何将嵌套列表转换为多维数组?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!