java 列出 Array Double[] 输入值
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List Arrary Double[] entering values
提问by Mark Worsnop
Using the examples below the 2nd part I see how to add values to a single dim array. But the 2 dim array I dont yet understand. In the 1st example the 1,2,3 I need to get from a database. The DB part I have figured out but how to put in the values I dont know. If I was using an array it would be
使用第二部分下面的示例，我了解了如何将值添加到单个昏暗数组中。但是我还不明白的 2 暗阵列。在第一个示例中，我需要从数据库中获取 1,2,3。我已经弄清楚了 DB 部分，但如何输入我不知道的值。如果我使用的是数组，它将是
myarray[row][column] = value;
so how do I do this with the List?
那么我该如何使用 List 做到这一点呢？
mylist.add --- something?
mylist.add --- 什么？
List<double []> // creates a list that stores arrays of doubles.
List<double []> myList = new ArrayList<Double>();
myList.add(new double [] {1,2,3});
myList.add(new double [] {4,5,6});
List<Double> myList = new ArrayList<Double>();
myList.add(1);
myList.add(2);
myList.add(3);
回答by
List<T> myList = new ArrayList<T>();
T should be same. If T is double[] then it should be new ArrayList<double[]>()
T 应该是一样的。如果 T 是 double[] 那么它应该是new ArrayList<double[]>()
then get(index)which is double array and get(index)[j]which is value. same logic with
那么get(index)哪个是双数组，get(index)[j]哪个是值。相同的逻辑
d[i][j] = get(index)[j]
d[i][j] = 获取（索引）[j]
List<double []> myList = new ArrayList<double[]>();
myList.add(new double [] {1,2,3});
myList.add(new double [] {4,5,6});
System.out.println(myList.get(0)[1]);
回答by Kevin Coppock
If you're talking about just doing inline initialization of a multidimensional array, I'm pretty sure you just use subsetted braces, like so:
如果您只是在谈论对多维数组进行内联初始化，我很确定您只是使用子集大括号，如下所示：
Double array2D[][] = {
{1, 2, 3},
{4, 5, 6},
{7, 8, 9}
};
回答by Mike Yockey
Do you want a collection-based solution for two-dimensional arrays? If so, then you're looking for a list of lists.
您想要二维数组的基于集合的解决方案吗？如果是这样，那么您正在寻找列表列表。
//Declaration
List<List<double[]>> twoDimList = new ArrayList<List<double>>();
//Adding values
twoDimList.add(new ArrayList<double>(1));
twoDimList.add(new ArrayList<double>(2));
twoDimList.add(new ArrayList<double>(3));
//Retrieving values
double value = twoDimList.get(1).get(1); //returns 1
回答by Laurence Gonsalves
You should avoid using arrays as generic type parameters as you can easily end up with "unchecked" warnings. Use collections (typically ArrayList) instead.
您应该避免使用数组作为泛型类型参数，因为您很容易以“未检查”警告结束。使用集合（通常ArrayList）代替。
So instead of this:
所以而不是这个：
List<double []> // creates a list that stores arrays of doubles.
List<double []> myList = new ArrayList<Double>();
myList.add(new double [] {1,2,3});
myList.add(new double [] {4,5,6});
Do something like this:
做这样的事情：
List<List<Double>> myList = new ArrayList<List<Double>>();
myList.add(new ArrayList<Double>());
myList.add(new ArrayList<Double>());
myList.get(0).add(1);
myList.get(0).add(2);
myList.get(0).add(3);
Or to initialize together, you'd probably do something like:
或者要一起初始化，您可能会执行以下操作：
List<List<Double>> myList = new ArrayList<List<Double>>();
List<Double> nested;
nested = new ArrayList<Double>();
nested.add(1);
nested.add(2);
nested.add(3);
myList.add(nested);
nested = new ArrayList<Double>();
nested.add(4);
nested.add(5);
nested.add(6);
myList.add(nested);
(You can add nestedto myListbefore or after adding the elements to nested-- either way works so do whatever is clearer to you.)
（您可以在将元素添加nested到myList之前或之后添加到nested- 无论哪种方式都有效，所以做任何对您来说更清楚的事情。）
To retrieve a specific element:
要检索特定元素：
double value = myList.get(x).get(y);
To set a specific element:
要设置特定元素：
myList.get(x).set(y, value);
This assumes that the list are already the right size, and that you just want to change the value of an existing element. (In other words, just like setbehaves on a simple List.)
这假设列表的大小已经合适，并且您只想更改现有元素的值。（换句话说，就像set在简单的List.上的行为一样。）
