What is the correct way to declare a multidimensional array and assign values to it?
This is what I have:
int x = 5;
int y = 5;
String[][] myStringA
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]);
}
}
}
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}
}
};
Java doesn't have "true" multidimensional arrays.
For example, arr[i][j][k]
is equivalent to ((arr[i])[j])[k]
. In other words, arr
is simply an array, of arrays, of arrays.
So, if you know how arrays work, you know how multidimensional arrays work!
Declaration:
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]]]"
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"}};
Try replacing the appropriate lines with:
myStringArray[0][x-1] = "a string";
myStringArray[0][y-1] = "another string";
Your code is incorrect because the sub-arrays have a length of y
, and indexing starts at 0. So setting to myStringArray[0][y]
or myStringArray[0][x]
will fail because the indices x
and y
are out of bounds.
String[][] myStringArray = new String [x][y];
is the correct way to initialise a rectangular multidimensional array. If you want it to be jagged (each sub-array potentially has a different length) then you can use code similar to this answer. Note however that John's assertion that you have to create the sub-arrays manually is incorrect in the case where you want a perfectly rectangular multidimensional array.