[英]How do i initialize a 2D Array with m(rows), n(cols) in java?
I wanted to initialize a 2D arraylist of size 2n-1(rows), n(cols)我想初始化一个大小为 2n-1(rows), n(cols) 的二维数组列表
int num = 3;
// declare an arrayList of ArrayLists or 2D ArrayList
ArrayList<ArrayList<Integer>> list =
new ArrayList<ArrayList<Integer>>(num);
The above syntax is to create 2D ArrayList of size Num*Num.上述语法是创建大小为 Num*Num 的 2D ArrayList。
In arrays we initialize with M*N, similarly can we do with ArrayLists?在我们用 M*N 初始化的数组中,我们可以用 ArrayLists 做类似的事情吗? if yes, how?
如果是,如何?
I want syntax to initialize with M*N.我想用 M*N 初始化语法。
Unlike an Array which must be initialized to a fixed length, an ArrayList can grow dynamically, you don't have to worry about M and N to initialize it.与必须初始化为固定长度的 Array 不同,ArrayList 可以动态增长,您不必担心M和N来初始化它。 You worry about that when you want to fill the ArrayList and if filling the collection to M and N is your specific requirement then do so after the ArrayList has been declared.
当您想要填充 ArrayList 并且如果将集合填充到M和N是您的特定要求时,您会担心,那么在声明 ArrayList 之后执行此操作。 So,
ArrayList<ArrayList<Integer>> list = new ArrayList<>();
所以,
ArrayList<ArrayList<Integer>> list = new ArrayList<>();
is all you need.是你所需要的全部。
There are a number of ways to fill the ArrayLists to your desired M (rows) and N (columns).有多种方法可以将 ArrayLists 填充到所需的M (行)和N (列)。 Here is a relatively decent visual way to do it.
这是一种相对不错的视觉方式。
ArrayList<ArrayList<Integer>> list = new ArrayList<>();
ArrayList<Integer> innerList;
int m = 20; // Rows
int n = 10; // Columns
int incrementer = 1;
for (int i = 0; i < m; i++) {
innerList = new ArrayList<>();
for (int j = 0; j < n; j++) {
innerList.add(j + incrementer);
}
list.add(innerList);
incrementer ++;
}
// Now to display (print) the 2D ArrayList into the Console Window:
for (ArrayList<Integer> inner : list) {
for (Integer ints : inner) {
System.out.printf("%-3s ", ints);
}
System.out.println();
}
The console should display:控制台应显示:
1 2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8 9 10 11
3 4 5 6 7 8 9 10 11 12
4 5 6 7 8 9 10 11 12 13
5 6 7 8 9 10 11 12 13 14
6 7 8 9 10 11 12 13 14 15
7 8 9 10 11 12 13 14 15 16
8 9 10 11 12 13 14 15 16 17
9 10 11 12 13 14 15 16 17 18
10 11 12 13 14 15 16 17 18 19
11 12 13 14 15 16 17 18 19 20
12 13 14 15 16 17 18 19 20 21
13 14 15 16 17 18 19 20 21 22
14 15 16 17 18 19 20 21 22 23
15 16 17 18 19 20 21 22 23 24
16 17 18 19 20 21 22 23 24 25
17 18 19 20 21 22 23 24 25 26
18 19 20 21 22 23 24 25 26 27
19 20 21 22 23 24 25 26 27 28
20 21 22 23 24 25 26 27 28 29
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