我如何循环彻底在Java 2D ArrayList和补吗？ [英] How do I loop thorough a 2D ArrayList in Java and fill it?

问题描述

我试图用2D的ArrayList Java编写的。
我的定义是：

I am trying to use 2D arrayLists in Java. I have the definition:

ArrayList<ArrayList<Integer>> myList = new ArrayList<ArrayList<Integer>>();

我怎么能环通过它，并从1开始的数字输入？
我知道我可以通过访问特定指数：

How can I loop through it and enter in numbers starting from 1? I know that I can access a specific index by using:

myList.get(i).get(j)

这将让该值。但我怎么添加到矩阵？

Which will get the value. But how do I add to the Matrix?

感谢

推荐答案

您可以使用嵌套的for循环。 i-循环遍历外ArrayList和第j环通过 myList中

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

for (int i = 0; i < myList.size(); i++)
{
    for (int j = 0; j < myList.get(i).size(); j++)
    {
        // do stuff
    } 
}

编辑：你再替换填充//做的东西与

myList.get(i).add(new Integer(YOUR_VALUE)); // append YOUR_VALUE to end of list

A注：如果myList中最初未填充，使用循环 .size（） 将无法正常工作作为你不能使用获得（SOME_INDEX）上的的ArrayList 不含指数。您将需要循环从0到要添加值的数量，在第一循环中创建一个新的列表，使用。新增（YOUR_VALUE）附加新价值在每次迭代到这个新的列表，然后添加新名单 myList中。请参见肯的回答一个很好的例子。

A Note: If the myList is initially unfilled, looping using .size() will not work as you cannot use .get(SOME_INDEX) on an ArrayList containing 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 answer for a perfect example.

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