問題描述
使用變量名作為數組索引 (Using variable name as array index)
I have few files which I put in array. I shuffle the files so that it can be displayed in random order. How to know that array index 0 is actually image1.txt or image2.txt or image3.txt? Thanks in advance.
String[] a = {"image1.txt","image2.txt","image3.txt"};
List<String> files = Arrays.asList(a);
Collections.shuffle(files);
‑‑‑‑‑
參考解法
方法 1:
I'm not sure what you are trying to do.
To access the first element of the shuffled list, use files.get(0).
If you want to know where each element is gone, I suggest you take another approach to it. Create a list of integers from 0 to a.length() ‑ 1, inclusive and shuffle that list. Then manually permute the array a to a new collection.
方法 2:
INCORRECT ‑ see explanation
Note: Arrays.asList() will create a NEW list with the contents of the passed array. The original array will not be modified at all when you use Collections.shuffle().
Explanation
Peter has correctly pointed our that Arrays.asList() does NOT make a copy. The returned list is "write‑through" back to the original array. Shuffling the list will shuffle the contents of the original array. Also worth noting that the list is immutable (new elements cannot be added) but typically I find that the use of Arrays.asList() involves immutable lists anyway.
files.get(0); // get the first elements in shuffled list, random
// as greg said
int index = files.indexOf(a[0]); // find out where "image1.txt" is in the list
files.get(index); // get "image1.txt" back from the list