如何在 Java 中遍历一个 2D ArrayList 并填充它？
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How do I loop thorough a 2D ArrayList in Java and fill it?
提问by user2955610
I am trying to use 2D arrayLists in Java. I have the definition:
我正在尝试在 Java 中使用 2D arrayLists。我有定义：
ArrayList<ArrayList<Integer>> myList = new ArrayList<ArrayList<Integer>>();
How can I loop through it and enter in numbers starting from 1? I know that I can access a specific index by using:
如何遍历它并输入从 1 开始的数字？我知道我可以使用以下方法访问特定索引：
myList.get(i).get(j)
Which will get the value. But how do I add to the Matrix?
哪个将获得价值。但是我如何添加到矩阵中？
Thanks
谢谢
回答by bpgeck
You can use a nested for loop. The i-loop loops through the outer ArrayList and the j-loop loops through each individual ArrayList contained by myList
您可以使用嵌套的 for 循环。i-loop 循环遍历外部 ArrayList，j-loop 循环遍历每个单独的 ArrayListmyList
for (int i = 0; i < myList.size(); i++)
{
for (int j = 0; j < myList.get(i).size(); j++)
{
// do stuff
}
}
Edit:you then fill it by replacing // do stuffwith
编辑：然后你用替换// do stuff来填充它
myList.get(i).add(new Integer(YOUR_VALUE)); // append YOUR_VALUE to end of list
A Note:If the myList is initially unfilled, looping using .size()will not workas you cannot use .get(SOME_INDEX)on an ArrayListcontaining no indices. You will need to loop from 0 to the number of values you wish to add, create a new list within the first loop, use .add(YOUR_VALUE)to append a new value on each iteration to this new list and then add this new list to myList. See Ken's answerfor a perfect example.
注意：如果 myList 最初未填充，则循环 using.size()将不起作用，因为您不能.get(SOME_INDEX)在不ArrayList包含索引的情况下使用。您需要从 0 循环到要添加的值的数量，在第一个循环中创建一个新列表，用于.add(YOUR_VALUE)在每次迭代时将新值附加到此新列表，然后将此新列表添加到myList. 有关完美示例，请参阅Ken 的回答。
回答by rajuGT
回答by Ken Geis
Assuming the matrix is not initialized,
假设矩阵未初始化，
int m = 10, n = 10;
ArrayList<ArrayList<Integer>> matrix = new ArrayList<ArrayList<Integer>>();
for (int i = 0; i < m; i++) {
List<Integer> row = new ArrayList<Integer>();
for (int j = 0; j < n; j++) {
row.add(j);
}
matrix.add(row);
}
