Wsrtjtyk

Say I had two randomly generated arrays (rows and columns) and I want them to be used to fill a multidimensional array. With the arrays being rows and columns, the multidimensional array would be matrix[rows][columns]. Just an example of how I generated rows:

int rows = new int[20];         

for(int i = 0; i < rows.length; i++) {

rows[i] = (int)(Math.random()*1000 + 1);

    }

System.out.println("Rows Generated: " + Arrays.toString(randomArrayN));

  }

}

The columns array was also built this way. Is there an easy way to create a two-dimension array and use these arrays to fill them?
I know this syntax is wrong but basically I want to know if there is a way to do this:

int matrix = new int[rows][columns];

If you need a 2d array filled with random ints, you can use a nested loop similar to what you used to genrate your rows above:

public static void main(String args) {

    int matrix = new int[20][20];

    for(int i = 0; i < matrix.length; i++){

        for(int j = 0; j < matrix[i].length; j++){

            matrix[i][j] = (int)(Math.random()*1000 + 1);

        }

    }



    for(int row : matrix){

        System.out.println(Arrays.toString(row));

    }        

}

Yea you definitely can, though it may be a bit more confusing.

You can initalize the 3d array with this:

// test is a 3d array

int test = {

          {

           {1, -2, 3}, 

           {2, 3, 4}

          }, 

          { 

           {-4, -5, 6, 9}, 

           {1}, 

           {2, 3}

          } 

};

I like to think this in terms or 3d obects, like a regtangluar prism. Each row (height)on the prism hold 2 things Length and Width, or a x,y. in other worlds you have a 2d array, one value is the column, the other is the row, in an array making it 3d.

now what if you want to print out values of the 3d array?
simply do this :

 for (int array2D: test) {

    for (int array1D: array2D) {

       for(int item: array1D) {

          System.out.println(item);

       }

    }

 }

Although it's convenient to think of a 2-dimensional array in terms of rows and columns, a 2-dimensional array is just an array of arrays.

For example,

    int values1 = {1, 2 ,3};

    int matrix1 = {values1, values1, values1};



    matrix1[1][1] = 42;

    System.out.println(matrix1[0][1]);

    System.out.println(matrix1[1][1]);

    System.out.println(matrix1[2][1]);

or

    int values2 = {1, 2 ,3};

    int matrix2 = new int[3][3];

    matrix2[0] = values2;

    matrix2[1] = values2;

    matrix2[2] = values2;



    matrix2[1][1] = 42;

    System.out.println(matrix2[0][1]);

    System.out.println(matrix2[1][1]);

    System.out.println(matrix2[2][1]);

Note that in both cases a values array is used multiple times to initialize each row of the matrix. So any change to any matrix element is reflected in the other rows (since each row is actually the same array). There may be cases where this is useful. If the elements need to be independent then use something like this:

    int values3 = {1, 2 ,3};

    int matrix3 = new int[3][3];

    System.arraycopy(values3, 0, matrix3[0], 0, values3.length);

    System.arraycopy(values3, 0, matrix3[1], 0, values3.length);

    System.arraycopy(values3, 0, matrix3[2], 0, values3.length);



    matrix3[1][1] = 42;

    System.out.println(matrix3[0][1]);

    System.out.println(matrix3[1][1]);

    System.out.println(matrix3[2][1]);

Each row of the matrix is initialized with a copy of the same value, but making changes to any element is independent of any other element (since it's a different array).

Also see this other question if the matrix needs to be initialized element by element.