Jaki jest prawidłowy sposób zadeklarowania tablicy wielowymiarowej i przypisania do niej wartości?
Oto co mam:
int x = 5;
int y = 5;
String[][] myStringArray = new String [x][y];
myStringArray[0][x] = "a string";
myStringArray[0][y] = "another string";
Odpowiedzi:
Spróbuj zamienić odpowiednie wiersze na:
myStringArray[0][x-1] = "a string";
myStringArray[0][y-1] = "another string";
Twój kod jest niepoprawny, ponieważ tablice podrzędne mają długość y, a indeksowanie zaczyna się od 0. Tak więc ustawienie myStringArray[0][y]lub myStringArray[0][x]nie powiedzie się, ponieważ indeksy xi ysą poza zakresem.
String[][] myStringArray = new String [x][y];jest prawidłowym sposobem inicjalizacji prostokątnej tablicy wielowymiarowej. Jeśli chcesz, aby była postrzępiona (każda podtablica ma potencjalnie inną długość), możesz użyć kodu podobnego do tej odpowiedzi . Zauważ jednak, że twierdzenie Johna, że musisz ręcznie tworzyć tablice podrzędne, jest niepoprawne w przypadku, gdy chcesz uzyskać idealnie prostokątną tablicę wielowymiarową.
Java nie ma „prawdziwych” wielowymiarowych tablic.
Na przykład arr[i][j][k]jest równoważne z ((arr[i])[j])[k]. Innymi słowy, arrjest po prostu tablicą, tablicami, tablicami .
Więc jeśli wiesz, jak działają tablice, wiesz, jak działają tablice wielowymiarowe!
Deklaracja:
int[][][] threeDimArr = new int[4][5][6];
or, with initialization:
int[][][] threeDimArr = { { { 1, 2 }, { 3, 4 } }, { { 5, 6 }, { 7, 8 } } };
Access:
int x = threeDimArr[1][0][1];
or
int[][] row = threeDimArr[1];
String representation:
Arrays.deepToString(threeDimArr);
yields
"[[[1, 2], [3, 4]], [[5, 6], [7, 8]]]"
int[i][j][k] has length i, so really it's equivalent to an ((int[k])[j])[i]. The sizes in the declaration are written backwards with respect to the types, I suppose to make multidimensional arrays more closely resemble matrices in mathematics.
You can declare multi dimensional arrays like :
// 4 x 5 String arrays, all Strings are null
// [0] -> [null,null,null,null,null]
// [1] -> [null,null,null,null,null]
// [2] -> [null,null,null,null,null]
// [3] -> [null,null,null,null,null]
String[][] sa1 = new String[4][5];
for(int i = 0; i < sa1.length; i++) { // sa1.length == 4
for (int j = 0; j < sa1[i].length; j++) { //sa1[i].length == 5
sa1[i][j] = "new String value";
}
}
// 5 x 0 All String arrays are null
// [null]
// [null]
// [null]
// [null]
// [null]
String[][] sa2 = new String[5][];
for(int i = 0; i < sa2.length; i++) {
String[] anon = new String[ /* your number here */];
// or String[] anon = new String[]{"I'm", "a", "new", "array"};
sa2[i] = anon;
}
// [0] -> ["I'm","in","the", "0th", "array"]
// [1] -> ["I'm", "in", "another"]
String[][] sa3 = new String[][]{ {"I'm","in","the", "0th", "array"},{"I'm", "in", "another"}};
Java does not truely support multidimensional arrays. In Java, a two-dimensional array is simply an array of arrays, a three-dimensional array is an array of arrays of arrays, a four-dimensional array is an array of arrays of arrays of arrays, and so on...
We can define a two-dimensional array as:
int[ ] num[ ] = {{1,2}, {1,2}, {1,2}, {1,2}}
int[ ][ ] num = new int[4][2]
num[0][0] = 1;
num[0][1] = 2;
num[1][0] = 1;
num[1][1] = 2;
num[2][0] = 1;
num[2][1] = 2;
num[3][0] = 1;
num[3][1] = 2;
If you don't allocate, let's say num[2][1], it is not initialized and then it is automatically allocated 0, that is, automatically num[2][1] = 0;
Below, num1.length gives you rows.
While num1[0].length gives you the number of elements related to num1[0]. Here num1[0] has related arrays num1[0][0] and num[0][1] only.
Here we used a for loop which helps us to calculate num1[i].length. Here i is incremented through a loop.
class array
{
static int[][] add(int[][] num1,int[][] num2)
{
int[][] temp = new int[num1.length][num1[0].length];
for(int i = 0; i<temp.length; i++)
{
for(int j = 0; j<temp[i].length; j++)
{
temp[i][j] = num1[i][j]+num2[i][j];
}
}
return temp;
}
public static void main(String args[])
{
/* We can define a two-dimensional array as
1. int[] num[] = {{1,2},{1,2},{1,2},{1,2}}
2. int[][] num = new int[4][2]
num[0][0] = 1;
num[0][1] = 2;
num[1][0] = 1;
num[1][1] = 2;
num[2][0] = 1;
num[2][1] = 2;
num[3][0] = 1;
num[3][1] = 2;
If you don't allocate let's say num[2][1] is
not initialized, and then it is automatically
allocated 0, that is, automatically num[2][1] = 0;
3. Below num1.length gives you rows
4. While num1[0].length gives you number of elements
related to num1[0]. Here num1[0] has related arrays
num1[0][0] and num[0][1] only.
5. Here we used a 'for' loop which helps us to calculate
num1[i].length, and here i is incremented through a loop.
*/
int num1[][] = {{1,2},{1,2},{1,2},{1,2}};
int num2[][] = {{1,2},{1,2},{1,2},{1,2}};
int num3[][] = add(num1,num2);
for(int i = 0; i<num1.length; i++)
{
for(int j = 0; j<num1[j].length; j++)
System.out.println("num3[" + i + "][" + j + "]=" + num3[i][j]);
}
}
}
I'll add that if you want to read the dimensions, you can do this:
int[][][] a = new int[4][3][2];
System.out.println(a.length); // 4
System.out.println(a[0].length); // 3
System.out.println(a[0][0].length); //2
You can also have jagged arrays, where different rows have different lengths, so a[0].length != a[1].length.
int[][] myNums = { {1, 2, 3, 4, 5, 6, 7}, {5, 6, 7, 8, 9, 10, 11} };
for (int x = 0; x < myNums.length; ++x) {
for(int y = 0; y < myNums[i].length; ++y) {
System.out.print(myNums[x][y]);
}
}
Output
1 2 3 4 5 6 7 5 6 7 8 9 10 11
You can look at this to start off:
int [][][] i = { //third dimension curly brace
{ // second dimension curly brace
{ //first dimension curly brace
1,1,1 //elements
},
{3,3,3},
{2,2,2}
},
{
{
1,1,1
},
{3,3,3},
{2,2,2}
}
};